pvc/node-daemon/pvcnoded/objects/NodeInstance.py

#!/usr/bin/env python3

# NodeInstance.py - Class implementing a PVC node in pvcnoded
# Part of the Parallel Virtual Cluster (PVC) system
#
#    Copyright (C) 2018-2021 Joshua M. Boniface <joshua@boniface.me>
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, version 3.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <https://www.gnu.org/licenses/>.
#
###############################################################################

import time

from threading import Thread, Event

import daemon_lib.common as common


class NodeInstance(object):
    # Initialization function
    def __init__(
        self,
        name,
        this_node,
        zkhandler,
        config,
        logger,
        d_node,
        d_network,
        d_domain,
        dns_aggregator,
        metadata_api,
    ):
        # Passed-in variables on creation
        self.name = name
        self.this_node = this_node
        self.zkhandler = zkhandler
        self.config = config
        self.logger = logger
        # Which node is primary
        self.primary_node = None
        # States
        self.daemon_mode = self.zkhandler.read(("node.mode", self.name))
        self.daemon_state = "stop"
        self.router_state = "client"
        self.domain_state = "flushed"
        # Object lists
        self.d_node = d_node
        self.d_network = d_network
        self.d_domain = d_domain
        self.dns_aggregator = dns_aggregator
        self.metadata_api = metadata_api
        # Printable lists
        self.active_node_list = []
        self.flushed_node_list = []
        self.inactive_node_list = []
        self.network_list = []
        self.domain_list = []
        # Node resources
        self.domains_count = 0
        self.memused = 0
        self.memfree = 0
        self.memalloc = 0
        self.vcpualloc = 0
        # Floating IP configurations
        if self.config["enable_networking"]:
            self.upstream_dev = self.config["upstream_dev"]
            self.upstream_floatingipaddr = self.config["upstream_floating_ip"].split(
                "/"
            )[0]
            self.upstream_ipaddr, self.upstream_cidrnetmask = self.config[
                "upstream_dev_ip"
            ].split("/")
            self.cluster_dev = self.config["cluster_dev"]
            self.cluster_floatingipaddr = self.config["cluster_floating_ip"].split("/")[
                0
            ]
            self.cluster_ipaddr, self.cluster_cidrnetmask = self.config[
                "cluster_dev_ip"
            ].split("/")
            self.storage_dev = self.config["storage_dev"]
            self.storage_floatingipaddr = self.config["storage_floating_ip"].split("/")[
                0
            ]
            self.storage_ipaddr, self.storage_cidrnetmask = self.config[
                "storage_dev_ip"
            ].split("/")
        else:
            self.upstream_dev = None
            self.upstream_floatingipaddr = None
            self.upstream_ipaddr = None
            self.upstream_cidrnetmask = None
            self.cluster_dev = None
            self.cluster_floatingipaddr = None
            self.cluster_ipaddr = None
            self.cluster_cidrnetmask = None
            self.storage_dev = None
            self.storage_floatingipaddr = None
            self.storage_ipaddr = None
            self.storage_cidrnetmask = None
        # Threads
        self.flush_thread = None
        self.flush_event = Event()
        # Flags
        self.flush_stopper = False

        # Zookeeper handlers for changed states
        @self.zkhandler.zk_conn.DataWatch(
            self.zkhandler.schema.path("node.state.daemon", self.name)
        )
        def watch_node_daemonstate(data, stat, event=""):
            if event and event.type == "DELETED":
                # The key has been deleted after existing before; terminate this watcher
                # because this class instance is about to be reaped in Daemon.py
                return False

            try:
                data = data.decode("ascii")
            except AttributeError:
                data = "stop"

            if data != self.daemon_state:
                self.daemon_state = data

        @self.zkhandler.zk_conn.DataWatch(
            self.zkhandler.schema.path("node.state.router", self.name)
        )
        def watch_node_routerstate(data, stat, event=""):
            if event and event.type == "DELETED":
                # The key has been deleted after existing before; terminate this watcher
                # because this class instance is about to be reaped in Daemon.py
                return False

            try:
                data = data.decode("ascii")
            except AttributeError:
                data = "client"

            if self.name == self.this_node and self.daemon_mode == "coordinator":
                # We're a coordinator so we care about networking
                if data != self.router_state:
                    self.router_state = data
                    if self.config["enable_networking"]:
                        if self.router_state == "takeover":
                            self.logger.out(
                                "Setting node {} to primary state".format(self.name),
                                state="i",
                            )
                            transition_thread = Thread(
                                target=self.become_primary, args=(), kwargs={}
                            )
                            transition_thread.start()
                        if self.router_state == "relinquish":
                            # Skip becoming secondary unless already running
                            if (
                                self.daemon_state == "run"
                                or self.daemon_state == "shutdown"
                            ):
                                self.logger.out(
                                    "Setting node {} to secondary state".format(
                                        self.name
                                    ),
                                    state="i",
                                )
                                transition_thread = Thread(
                                    target=self.become_secondary, args=(), kwargs={}
                                )
                                transition_thread.start()
                            else:
                                # We did nothing, so just become secondary state
                                self.zkhandler.write(
                                    [(("node.state.router", self.name), "secondary")]
                                )

        @self.zkhandler.zk_conn.DataWatch(
            self.zkhandler.schema.path("node.state.domain", self.name)
        )
        def watch_node_domainstate(data, stat, event=""):
            if event and event.type == "DELETED":
                # The key has been deleted after existing before; terminate this watcher
                # because this class instance is about to be reaped in Daemon.py
                return False

            try:
                data = data.decode("ascii")
            except AttributeError:
                data = "unknown"

            if data != self.domain_state:
                self.domain_state = data

                # toggle state management of this node
                if self.name == self.this_node:
                    # Stop any existing flush jobs
                    if self.flush_thread is not None:
                        self.logger.out(
                            "Waiting for previous migration to complete".format(
                                self.name
                            ),
                            state="i",
                        )
                        self.flush_stopper = True
                        self.flush_event.wait()
                        self.flush_event.clear()

                    # Do flushing in a thread so it doesn't block the migrates out
                    if self.domain_state == "flush":
                        self.flush_thread = Thread(
                            target=self.flush, args=(), kwargs={}
                        )
                        self.flush_thread.start()
                    # Do unflushing in a thread so it doesn't block the migrates in
                    if self.domain_state == "unflush":
                        self.flush_thread = Thread(
                            target=self.unflush, args=(), kwargs={}
                        )
                        self.flush_thread.start()

        @self.zkhandler.zk_conn.DataWatch(
            self.zkhandler.schema.path("node.memory.free", self.name)
        )
        def watch_node_memfree(data, stat, event=""):
            if event and event.type == "DELETED":
                # The key has been deleted after existing before; terminate this watcher
                # because this class instance is about to be reaped in Daemon.py
                return False

            try:
                data = data.decode("ascii")
            except AttributeError:
                data = 0

            if data != self.memfree:
                self.memfree = data

        @self.zkhandler.zk_conn.DataWatch(
            self.zkhandler.schema.path("node.memory.used", self.name)
        )
        def watch_node_memused(data, stat, event=""):
            if event and event.type == "DELETED":
                # The key has been deleted after existing before; terminate this watcher
                # because this class instance is about to be reaped in Daemon.py
                return False

            try:
                data = data.decode("ascii")
            except AttributeError:
                data = 0

            if data != self.memused:
                self.memused = data

        @self.zkhandler.zk_conn.DataWatch(
            self.zkhandler.schema.path("node.memory.allocated", self.name)
        )
        def watch_node_memalloc(data, stat, event=""):
            if event and event.type == "DELETED":
                # The key has been deleted after existing before; terminate this watcher
                # because this class instance is about to be reaped in Daemon.py
                return False

            try:
                data = data.decode("ascii")
            except AttributeError:
                data = 0

            if data != self.memalloc:
                self.memalloc = data

        @self.zkhandler.zk_conn.DataWatch(
            self.zkhandler.schema.path("node.vcpu.allocated", self.name)
        )
        def watch_node_vcpualloc(data, stat, event=""):
            if event and event.type == "DELETED":
                # The key has been deleted after existing before; terminate this watcher
                # because this class instance is about to be reaped in Daemon.py
                return False

            try:
                data = data.decode("ascii")
            except AttributeError:
                data = 0

            if data != self.vcpualloc:
                self.vcpualloc = data

        @self.zkhandler.zk_conn.DataWatch(
            self.zkhandler.schema.path("node.running_domains", self.name)
        )
        def watch_node_runningdomains(data, stat, event=""):
            if event and event.type == "DELETED":
                # The key has been deleted after existing before; terminate this watcher
                # because this class instance is about to be reaped in Daemon.py
                return False

            try:
                data = data.decode("ascii").split()
            except AttributeError:
                data = []

            if data != self.domain_list:
                self.domain_list = data

        @self.zkhandler.zk_conn.DataWatch(
            self.zkhandler.schema.path("node.count.provisioned_domains", self.name)
        )
        def watch_node_domainscount(data, stat, event=""):
            if event and event.type == "DELETED":
                # The key has been deleted after existing before; terminate this watcher
                # because this class instance is about to be reaped in Daemon.py
                return False

            try:
                data = data.decode("ascii")
            except AttributeError:
                data = 0

            if data != self.domains_count:
                self.domains_count = data

    # Update value functions
    def update_node_list(self, d_node):
        self.d_node = d_node

    def update_network_list(self, d_network):
        self.d_network = d_network
        network_list = []
        for network in self.d_network:
            network_list.append(d_network[network].vni)
        self.network_list = network_list

    def update_domain_list(self, d_domain):
        self.d_domain = d_domain

    ######
    # Phases of node transition
    #
    # Current Primary                   Candidate Secondary
    #   -> secondary                      -> primary
    #
    # def become_secondary()            def become_primary()
    #
    # A ----------------------------------------------------------------- SYNC (candidate)
    # B ----------------------------------------------------------------- SYNC (current)
    # 1. Stop DNS aggregator                                               ||
    # 2. Stop DHCP servers                                                 ||
    #    4a) network 1                                                     ||
    #    4b) network 2                                                     ||
    #    etc.                                                              ||
    # 3. Stop client API                                                   ||
    # 4. Stop metadata API                                                 ||
    #                                                                      --
    # C ----------------------------------------------------------------- SYNC (candidate)
    # 5. Remove upstream floating IP    1. Add upstream floating IP        ||
    #                                                                      --
    # D ----------------------------------------------------------------- SYNC (candidate)
    # 6. Remove cluster floating IP     2. Add cluster floating IP         ||
    #                                                                      --
    # E ----------------------------------------------------------------- SYNC (candidate)
    # 7. Remove metadata floating IP    3. Add metadata floating IP        ||
    #                                                                      --
    # F ----------------------------------------------------------------- SYNC (candidate)
    # 8. Remove gateway IPs             4. Add gateway IPs                 ||
    #    8a) network 1                     4a) network 1                   ||
    #    8b) network 2                     4b) network 2                   ||
    #    etc.                              etc.                            ||
    #                                                                      --
    # G ----------------------------------------------------------------- SYNC (candidate)
    #                                   5. Transition Patroni primary      ||
    #                                   6. Start client API                ||
    #                                   7. Start metadata API              ||
    #                                   8. Start DHCP servers              ||
    #                                      5a) network 1                   ||
    #                                      5b) network 2                   ||
    #                                      etc.                            ||
    #                                   9. Start DNS aggregator            ||
    #                                                                      --
    ######
    def become_primary(self):
        """
        Acquire primary coordinator status from a peer node
        """
        # Lock the primary node until transition is complete
        primary_lock = self.zkhandler.exclusivelock("base.config.primary_node")
        primary_lock.acquire()

        # Ensure our lock key is populated
        self.zkhandler.write([("base.config.primary_node.sync_lock", "")])

        # Synchronize nodes A (I am writer)
        lock = self.zkhandler.writelock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring write lock for synchronization phase A", state="i")
        lock.acquire()
        self.logger.out("Acquired write lock for synchronization phase A", state="o")
        time.sleep(1)  # Time fir reader to acquire the lock
        self.logger.out("Releasing write lock for synchronization phase A", state="i")
        self.zkhandler.write([("base.config.primary_node.sync_lock", "")])
        lock.release()
        self.logger.out("Released write lock for synchronization phase A", state="o")
        time.sleep(0.1)  # Time fir new writer to acquire the lock

        # Synchronize nodes B (I am reader)
        lock = self.zkhandler.readlock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring read lock for synchronization phase B", state="i")
        lock.acquire()
        self.logger.out("Acquired read lock for synchronization phase B", state="o")
        self.logger.out("Releasing read lock for synchronization phase B", state="i")
        lock.release()
        self.logger.out("Released read lock for synchronization phase B", state="o")

        # Synchronize nodes C (I am writer)
        lock = self.zkhandler.writelock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring write lock for synchronization phase C", state="i")
        lock.acquire()
        self.logger.out("Acquired write lock for synchronization phase C", state="o")
        time.sleep(0.5)  # Time fir reader to acquire the lock
        # 1. Add Upstream floating IP
        self.logger.out(
            "Creating floating upstream IP {}/{} on interface {}".format(
                self.upstream_floatingipaddr, self.upstream_cidrnetmask, "brupstream"
            ),
            state="o",
        )
        common.createIPAddress(
            self.upstream_floatingipaddr, self.upstream_cidrnetmask, "brupstream"
        )
        self.logger.out("Releasing write lock for synchronization phase C", state="i")
        self.zkhandler.write([("base.config.primary_node.sync_lock", "")])
        lock.release()
        self.logger.out("Released write lock for synchronization phase C", state="o")

        # Synchronize nodes D (I am writer)
        lock = self.zkhandler.writelock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring write lock for synchronization phase D", state="i")
        lock.acquire()
        self.logger.out("Acquired write lock for synchronization phase D", state="o")
        time.sleep(0.2)  # Time fir reader to acquire the lock
        # 2. Add Cluster & Storage floating IP
        self.logger.out(
            "Creating floating management IP {}/{} on interface {}".format(
                self.cluster_floatingipaddr, self.cluster_cidrnetmask, "brcluster"
            ),
            state="o",
        )
        common.createIPAddress(
            self.cluster_floatingipaddr, self.cluster_cidrnetmask, "brcluster"
        )
        self.logger.out(
            "Creating floating storage IP {}/{} on interface {}".format(
                self.storage_floatingipaddr, self.storage_cidrnetmask, "brstorage"
            ),
            state="o",
        )
        common.createIPAddress(
            self.storage_floatingipaddr, self.storage_cidrnetmask, "brstorage"
        )
        self.logger.out("Releasing write lock for synchronization phase D", state="i")
        self.zkhandler.write([("base.config.primary_node.sync_lock", "")])
        lock.release()
        self.logger.out("Released write lock for synchronization phase D", state="o")

        # Synchronize nodes E (I am writer)
        lock = self.zkhandler.writelock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring write lock for synchronization phase E", state="i")
        lock.acquire()
        self.logger.out("Acquired write lock for synchronization phase E", state="o")
        time.sleep(0.2)  # Time fir reader to acquire the lock
        # 3. Add Metadata link-local IP
        self.logger.out(
            "Creating Metadata link-local IP {}/{} on interface {}".format(
                "169.254.169.254", "32", "lo"
            ),
            state="o",
        )
        common.createIPAddress("169.254.169.254", "32", "lo")
        self.logger.out("Releasing write lock for synchronization phase E", state="i")
        self.zkhandler.write([("base.config.primary_node.sync_lock", "")])
        lock.release()
        self.logger.out("Released write lock for synchronization phase E", state="o")

        # Synchronize nodes F (I am writer)
        lock = self.zkhandler.writelock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring write lock for synchronization phase F", state="i")
        lock.acquire()
        self.logger.out("Acquired write lock for synchronization phase F", state="o")
        time.sleep(0.2)  # Time fir reader to acquire the lock
        # 4. Add gateway IPs
        for network in self.d_network:
            self.d_network[network].createGateways()
        self.logger.out("Releasing write lock for synchronization phase F", state="i")
        self.zkhandler.write([("base.config.primary_node.sync_lock", "")])
        lock.release()
        self.logger.out("Released write lock for synchronization phase F", state="o")

        # Synchronize nodes G (I am writer)
        lock = self.zkhandler.writelock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring write lock for synchronization phase G", state="i")
        lock.acquire()
        self.logger.out("Acquired write lock for synchronization phase G", state="o")
        time.sleep(0.2)  # Time fir reader to acquire the lock
        # 5. Transition Patroni primary
        self.logger.out("Setting Patroni leader to this node", state="i")
        tick = 1
        patroni_failed = True
        # As long as we're in takeover, keep trying to set the Patroni leader to us
        while self.router_state == "takeover":
            # Switch Patroni leader to the local instance
            retcode, stdout, stderr = common.run_os_command(
                """
                patronictl
                    -c /etc/patroni/config.yml
                    switchover
                    --candidate {}
                    --force
                    pvc
                """.format(
                    self.name
                )
            )

            # Combine the stdout and stderr and strip the output
            # Patronictl's output is pretty junky
            if stderr:
                stdout += stderr
            stdout = stdout.strip()

            # Handle our current Patroni leader being us
            if stdout and stdout.split("\n")[-1].split() == [
                "Error:",
                "Switchover",
                "target",
                "and",
                "source",
                "are",
                "the",
                "same.",
            ]:
                self.logger.out(
                    "Failed to switch Patroni leader to ourselves; this is fine\n{}".format(
                        stdout
                    ),
                    state="w",
                )
                patroni_failed = False
                break
            # Handle a failed switchover
            elif stdout and (
                stdout.split("\n")[-1].split()[:2] == ["Switchover", "failed,"]
                or stdout.strip().split("\n")[-1].split()[:1] == ["Error"]
            ):
                if tick > 4:
                    self.logger.out(
                        "Failed to switch Patroni leader after 5 tries; aborting",
                        state="e",
                    )
                    break
                else:
                    self.logger.out(
                        "Failed to switch Patroni leader; retrying [{}/5]\n{}\n".format(
                            tick, stdout
                        ),
                        state="e",
                    )
                    tick += 1
                    time.sleep(5)
            # Otherwise, we succeeded
            else:
                self.logger.out(
                    "Successfully switched Patroni leader\n{}".format(stdout), state="o"
                )
                patroni_failed = False
                time.sleep(0.2)
                break
        # 6. Start client API (and provisioner worker)
        if self.config["enable_api"]:
            self.logger.out("Starting PVC API client service", state="i")
            common.run_os_command("systemctl enable pvcapid.service")
            common.run_os_command("systemctl start pvcapid.service")
            self.logger.out("Starting PVC Provisioner Worker service", state="i")
            common.run_os_command("systemctl start pvcapid-worker.service")
        # 7. Start metadata API; just continue if we fail
        self.metadata_api.start()
        # 8. Start DHCP servers
        for network in self.d_network:
            self.d_network[network].startDHCPServer()
        # 9. Start DNS aggregator; just continue if we fail
        if not patroni_failed:
            self.dns_aggregator.start_aggregator()
        else:
            self.logger.out(
                "Not starting DNS aggregator due to Patroni failures", state="e"
            )
        self.logger.out("Releasing write lock for synchronization phase G", state="i")
        self.zkhandler.write([("base.config.primary_node.sync_lock", "")])
        lock.release()
        self.logger.out("Released write lock for synchronization phase G", state="o")

        # Wait 2 seconds for everything to stabilize before we declare all-done
        time.sleep(2)
        primary_lock.release()
        self.zkhandler.write([(("node.state.router", self.name), "primary")])
        self.logger.out(
            "Node {} transitioned to primary state".format(self.name), state="o"
        )

    def become_secondary(self):
        """
        Relinquish primary coordinator status to a peer node
        """
        time.sleep(0.2)  # Initial delay for the first writer to grab the lock

        # Synchronize nodes A (I am reader)
        lock = self.zkhandler.readlock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring read lock for synchronization phase A", state="i")
        lock.acquire()
        self.logger.out("Acquired read lock for synchronization phase A", state="o")
        self.logger.out("Releasing read lock for synchronization phase A", state="i")
        lock.release()
        self.logger.out("Released read lock for synchronization phase A", state="o")

        # Synchronize nodes B (I am writer)
        lock = self.zkhandler.writelock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring write lock for synchronization phase B", state="i")
        lock.acquire()
        self.logger.out("Acquired write lock for synchronization phase B", state="o")
        time.sleep(0.2)  # Time fir reader to acquire the lock
        # 1. Stop DNS aggregator
        self.dns_aggregator.stop_aggregator()
        # 2. Stop DHCP servers
        for network in self.d_network:
            self.d_network[network].stopDHCPServer()
        self.logger.out("Releasing write lock for synchronization phase B", state="i")
        self.zkhandler.write([("base.config.primary_node.sync_lock", "")])
        lock.release()
        self.logger.out("Released write lock for synchronization phase B", state="o")
        # 3. Stop client API
        if self.config["enable_api"]:
            self.logger.out("Stopping PVC API client service", state="i")
            common.run_os_command("systemctl stop pvcapid.service")
            common.run_os_command("systemctl disable pvcapid.service")
        # 4. Stop metadata API
        self.metadata_api.stop()
        time.sleep(0.1)  # Time fir new writer to acquire the lock

        # Synchronize nodes C (I am reader)
        lock = self.zkhandler.readlock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring read lock for synchronization phase C", state="i")
        lock.acquire()
        self.logger.out("Acquired read lock for synchronization phase C", state="o")
        # 5. Remove Upstream floating IP
        self.logger.out(
            "Removing floating upstream IP {}/{} from interface {}".format(
                self.upstream_floatingipaddr, self.upstream_cidrnetmask, "brupstream"
            ),
            state="o",
        )
        common.removeIPAddress(
            self.upstream_floatingipaddr, self.upstream_cidrnetmask, "brupstream"
        )
        self.logger.out("Releasing read lock for synchronization phase C", state="i")
        lock.release()
        self.logger.out("Released read lock for synchronization phase C", state="o")

        # Synchronize nodes D (I am reader)
        lock = self.zkhandler.readlock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring read lock for synchronization phase D", state="i")
        lock.acquire()
        self.logger.out("Acquired read lock for synchronization phase D", state="o")
        # 6. Remove Cluster & Storage floating IP
        self.logger.out(
            "Removing floating management IP {}/{} from interface {}".format(
                self.cluster_floatingipaddr, self.cluster_cidrnetmask, "brcluster"
            ),
            state="o",
        )
        common.removeIPAddress(
            self.cluster_floatingipaddr, self.cluster_cidrnetmask, "brcluster"
        )
        self.logger.out(
            "Removing floating storage IP {}/{} from interface {}".format(
                self.storage_floatingipaddr, self.storage_cidrnetmask, "brstorage"
            ),
            state="o",
        )
        common.removeIPAddress(
            self.storage_floatingipaddr, self.storage_cidrnetmask, "brstorage"
        )
        self.logger.out("Releasing read lock for synchronization phase D", state="i")
        lock.release()
        self.logger.out("Released read lock for synchronization phase D", state="o")

        # Synchronize nodes E (I am reader)
        lock = self.zkhandler.readlock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring read lock for synchronization phase E", state="i")
        lock.acquire()
        self.logger.out("Acquired read lock for synchronization phase E", state="o")
        # 7. Remove Metadata link-local IP
        self.logger.out(
            "Removing Metadata link-local IP {}/{} from interface {}".format(
                "169.254.169.254", "32", "lo"
            ),
            state="o",
        )
        common.removeIPAddress("169.254.169.254", "32", "lo")
        self.logger.out("Releasing read lock for synchronization phase E", state="i")
        lock.release()
        self.logger.out("Released read lock for synchronization phase E", state="o")

        # Synchronize nodes F (I am reader)
        lock = self.zkhandler.readlock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring read lock for synchronization phase F", state="i")
        lock.acquire()
        self.logger.out("Acquired read lock for synchronization phase F", state="o")
        # 8. Remove gateway IPs
        for network in self.d_network:
            self.d_network[network].removeGateways()
        self.logger.out("Releasing read lock for synchronization phase F", state="i")
        lock.release()
        self.logger.out("Released read lock for synchronization phase F", state="o")

        # Synchronize nodes G (I am reader)
        lock = self.zkhandler.readlock("base.config.primary_node.sync_lock")
        self.logger.out("Acquiring read lock for synchronization phase G", state="i")
        try:
            lock.acquire(timeout=60)  # Don't wait forever and completely block us
            self.logger.out("Acquired read lock for synchronization phase G", state="o")
        except Exception:
            pass
        self.logger.out("Releasing read lock for synchronization phase G", state="i")
        lock.release()
        self.logger.out("Released read lock for synchronization phase G", state="o")

        # Wait 2 seconds for everything to stabilize before we declare all-done
        time.sleep(2)
        self.zkhandler.write([(("node.state.router", self.name), "secondary")])
        self.logger.out(
            "Node {} transitioned to secondary state".format(self.name), state="o"
        )

    # Flush all VMs on the host
    def flush(self):
        # Begin flush
        self.logger.out(
            'Flushing node "{}" of running VMs'.format(self.name), state="i"
        )
        self.logger.out("VM list: {}".format(", ".join(self.domain_list)), state="i")
        fixed_domain_list = self.domain_list.copy()
        for dom_uuid in fixed_domain_list:
            # Allow us to cancel the operation
            if self.flush_stopper:
                self.logger.out("Aborting node flush".format(self.name), state="i")
                self.flush_event.set()
                self.flush_thread = None
                self.flush_stopper = False
                return

            self.logger.out(
                'Selecting target to migrate VM "{}"'.format(dom_uuid), state="i"
            )

            # Don't replace the previous node if the VM is already migrated
            if self.zkhandler.read(("domain.last_node", dom_uuid)):
                current_node = self.zkhandler.read(("domain.last_node", dom_uuid))
            else:
                current_node = self.zkhandler.read(("domain.node", dom_uuid))

            target_node = common.findTargetNode(self.zkhandler, dom_uuid)
            if target_node == current_node:
                target_node = None

            if target_node is None:
                self.logger.out(
                    'Failed to find migration target for VM "{}"; shutting down and setting autostart flag'.format(
                        dom_uuid
                    ),
                    state="e",
                )
                self.zkhandler.write(
                    [
                        (("domain.state", dom_uuid), "shutdown"),
                        (("domain.meta.autostart", dom_uuid), "True"),
                    ]
                )
            else:
                self.logger.out(
                    'Migrating VM "{}" to node "{}"'.format(dom_uuid, target_node),
                    state="i",
                )
                self.zkhandler.write(
                    [
                        (("domain.state", dom_uuid), "migrate"),
                        (("domain.node", dom_uuid), target_node),
                        (("domain.last_node", dom_uuid), current_node),
                    ]
                )

            # Wait for the VM to migrate so the next VM's free RAM count is accurate (they migrate in serial anyways)
            ticks = 0
            self.logger.out(
                'Waiting for migration of VM "{}"'.format(dom_uuid), state="i"
            )
            while self.zkhandler.read(("domain.state", dom_uuid)) in [
                "migrate",
                "unmigrate",
                "shutdown",
            ]:
                ticks += 1
                if ticks > 600:
                    # Abort if we've waited for 120 seconds, the VM is messed and just continue
                    break
                time.sleep(0.2)

        self.zkhandler.write(
            [
                (("node.running_domains", self.name), ""),
                (("node.state.domain", self.name), "flushed"),
            ]
        )
        self.flush_thread = None
        self.flush_stopper = False
        return

    def unflush(self):
        self.logger.out(
            "Restoring node {} to active service.".format(self.name), state="i"
        )
        fixed_domain_list = self.d_domain.copy()
        for dom_uuid in fixed_domain_list:
            # Allow us to cancel the operation
            if self.flush_stopper:
                self.logger.out("Aborting node unflush".format(self.name), state="i")
                self.flush_event.set()
                self.flush_thread = None
                self.flush_stopper = False
                return

            # Handle autostarts
            autostart = self.zkhandler.read(("domain.meta.autostart", dom_uuid))
            node = self.zkhandler.read(("domain.node", dom_uuid))
            if autostart == "True" and node == self.name:
                self.logger.out(
                    'Starting autostart VM "{}"'.format(dom_uuid), state="i"
                )
                self.zkhandler.write(
                    [
                        (("domain.state", dom_uuid), "start"),
                        (("domain.node", dom_uuid), self.name),
                        (("domain.last_node", dom_uuid), ""),
                        (("domain.meta.autostart", dom_uuid), "False"),
                    ]
                )
                continue

            try:
                last_node = self.zkhandler.read(("domain.last_node", dom_uuid))
            except Exception:
                continue

            if last_node != self.name:
                continue

            self.logger.out(
                'Setting unmigration for VM "{}"'.format(dom_uuid), state="i"
            )
            self.zkhandler.write(
                [
                    (("domain.state", dom_uuid), "migrate"),
                    (("domain.node", dom_uuid), self.name),
                    (("domain.last_node", dom_uuid), ""),
                ]
            )

            # Wait for the VM to migrate back
            ticks = 0
            self.logger.out(
                'Waiting for migration of VM "{}"'.format(dom_uuid), state="i"
            )
            while self.zkhandler.read(("domain.state", dom_uuid)) in [
                "migrate",
                "unmigrate",
                "shutdown",
            ]:
                ticks += 1
                if ticks > 600:
                    # Abort if we've waited for 120 seconds, the VM is messed and just continue
                    break
                time.sleep(0.2)

        self.zkhandler.write([(("node.state.domain", self.name), "ready")])
        self.flush_thread = None
        self.flush_stopper = False
        return