path: root/redis/sentinel.py

import random
import weakref

from redis.client import Redis
from redis.commands import SentinelCommands
from redis.connection import Connection, ConnectionPool, SSLConnection
from redis.exceptions import ConnectionError, ReadOnlyError, ResponseError, TimeoutError
from redis.utils import str_if_bytes


class MasterNotFoundError(ConnectionError):
    pass


class SlaveNotFoundError(ConnectionError):
    pass


class SentinelManagedConnection(Connection):
    def __init__(self, **kwargs):
        self.connection_pool = kwargs.pop("connection_pool")
        super().__init__(**kwargs)

    def __repr__(self):
        pool = self.connection_pool
        s = f"{type(self).__name__}<service={pool.service_name}%s>"
        if self.host:
            host_info = f",host={self.host},port={self.port}"
            s = s % host_info
        return s

    def connect_to(self, address):
        self.host, self.port = address
        super().connect()
        if self.connection_pool.check_connection:
            self.send_command("PING")
            if str_if_bytes(self.read_response()) != "PONG":
                raise ConnectionError("PING failed")

    def _connect_retry(self):
        if self._sock:
            return  # already connected
        if self.connection_pool.is_master:
            self.connect_to(self.connection_pool.get_master_address())
        else:
            for slave in self.connection_pool.rotate_slaves():
                try:
                    return self.connect_to(slave)
                except ConnectionError:
                    continue
            raise SlaveNotFoundError  # Never be here

    def connect(self):
        return self.retry.call_with_retry(
            self._connect_retry,
            lambda error: None,
        )

    def read_response(self, disable_decoding=False):
        try:
            return super().read_response(disable_decoding=disable_decoding)
        except ReadOnlyError:
            if self.connection_pool.is_master:
                # When talking to a master, a ReadOnlyError when likely
                # indicates that the previous master that we're still connected
                # to has been demoted to a slave and there's a new master.
                # calling disconnect will force the connection to re-query
                # sentinel during the next connect() attempt.
                self.disconnect()
                raise ConnectionError("The previous master is now a slave")
            raise


class SentinelManagedSSLConnection(SentinelManagedConnection, SSLConnection):
    pass


class SentinelConnectionPool(ConnectionPool):
    """
    Sentinel backed connection pool.

    If ``check_connection`` flag is set to True, SentinelManagedConnection
    sends a PING command right after establishing the connection.
    """

    def __init__(self, service_name, sentinel_manager, **kwargs):
        kwargs["connection_class"] = kwargs.get(
            "connection_class",
            SentinelManagedSSLConnection
            if kwargs.pop("ssl", False)
            else SentinelManagedConnection,
        )
        self.is_master = kwargs.pop("is_master", True)
        self.check_connection = kwargs.pop("check_connection", False)
        super().__init__(**kwargs)
        self.connection_kwargs["connection_pool"] = weakref.proxy(self)
        self.service_name = service_name
        self.sentinel_manager = sentinel_manager

    def __repr__(self):
        role = "master" if self.is_master else "slave"
        return f"{type(self).__name__}<service={self.service_name}({role})"

    def reset(self):
        super().reset()
        self.master_address = None
        self.slave_rr_counter = None

    def owns_connection(self, connection):
        check = not self.is_master or (
            self.is_master and self.master_address == (connection.host, connection.port)
        )
        parent = super()
        return check and parent.owns_connection(connection)

    def get_master_address(self):
        master_address = self.sentinel_manager.discover_master(self.service_name)
        if self.is_master:
            if self.master_address != master_address:
                self.master_address = master_address
                # disconnect any idle connections so that they reconnect
                # to the new master the next time that they are used.
                self.disconnect(inuse_connections=False)
        return master_address

    def rotate_slaves(self):
        "Round-robin slave balancer"
        slaves = self.sentinel_manager.discover_slaves(self.service_name)
        if slaves:
            if self.slave_rr_counter is None:
                self.slave_rr_counter = random.randint(0, len(slaves) - 1)
            for _ in range(len(slaves)):
                self.slave_rr_counter = (self.slave_rr_counter + 1) % len(slaves)
                slave = slaves[self.slave_rr_counter]
                yield slave
        # Fallback to the master connection
        try:
            yield self.get_master_address()
        except MasterNotFoundError:
            pass
        raise SlaveNotFoundError(f"No slave found for {self.service_name!r}")


class Sentinel(SentinelCommands):
    """
    Redis Sentinel cluster client

    >>> from redis.sentinel import Sentinel
    >>> sentinel = Sentinel([('localhost', 26379)], socket_timeout=0.1)
    >>> master = sentinel.master_for('mymaster', socket_timeout=0.1)
    >>> master.set('foo', 'bar')
    >>> slave = sentinel.slave_for('mymaster', socket_timeout=0.1)
    >>> slave.get('foo')
    b'bar'

    ``sentinels`` is a list of sentinel nodes. Each node is represented by
    a pair (hostname, port).

    ``min_other_sentinels`` defined a minimum number of peers for a sentinel.
    When querying a sentinel, if it doesn't meet this threshold, responses
    from that sentinel won't be considered valid.

    ``sentinel_kwargs`` is a dictionary of connection arguments used when
    connecting to sentinel instances. Any argument that can be passed to
    a normal Redis connection can be specified here. If ``sentinel_kwargs`` is
    not specified, any socket_timeout and socket_keepalive options specified
    in ``connection_kwargs`` will be used.

    ``connection_kwargs`` are keyword arguments that will be used when
    establishing a connection to a Redis server.
    """

    def __init__(
        self,
        sentinels,
        min_other_sentinels=0,
        sentinel_kwargs=None,
        **connection_kwargs,
    ):
        # if sentinel_kwargs isn't defined, use the socket_* options from
        # connection_kwargs
        if sentinel_kwargs is None:
            sentinel_kwargs = {
                k: v for k, v in connection_kwargs.items() if k.startswith("socket_")
            }
        self.sentinel_kwargs = sentinel_kwargs

        self.sentinels = [
            Redis(hostname, port, **self.sentinel_kwargs)
            for hostname, port in sentinels
        ]
        self.min_other_sentinels = min_other_sentinels
        self.connection_kwargs = connection_kwargs

    def execute_command(self, *args, **kwargs):
        """
        Execute Sentinel command in sentinel nodes.
        once - If set to True, then execute the resulting command on a single
        node at random, rather than across the entire sentinel cluster.
        """
        once = bool(kwargs.get("once", False))
        if "once" in kwargs.keys():
            kwargs.pop("once")

        if once:
            for sentinel in self.sentinels:
                sentinel.execute_command(*args, **kwargs)
        else:
            random.choice(self.sentinels).execute_command(*args, **kwargs)
        return True

    def __repr__(self):
        sentinel_addresses = []
        for sentinel in self.sentinels:
            sentinel_addresses.append(
                "{host}:{port}".format_map(
                    sentinel.connection_pool.connection_kwargs,
                )
            )
        return f'{type(self).__name__}<sentinels=[{",".join(sentinel_addresses)}]>'

    def check_master_state(self, state, service_name):
        if not state["is_master"] or state["is_sdown"] or state["is_odown"]:
            return False
        # Check if our sentinel doesn't see other nodes
        if state["num-other-sentinels"] < self.min_other_sentinels:
            return False
        return True

    def discover_master(self, service_name):
        """
        Asks sentinel servers for the Redis master's address corresponding
        to the service labeled ``service_name``.

        Returns a pair (address, port) or raises MasterNotFoundError if no
        master is found.
        """
        for sentinel_no, sentinel in enumerate(self.sentinels):
            try:
                masters = sentinel.sentinel_masters()
            except (ConnectionError, TimeoutError):
                continue
            state = masters.get(service_name)
            if state and self.check_master_state(state, service_name):
                # Put this sentinel at the top of the list
                self.sentinels[0], self.sentinels[sentinel_no] = (
                    sentinel,
                    self.sentinels[0],
                )
                return state["ip"], state["port"]
        raise MasterNotFoundError(f"No master found for {service_name!r}")

    def filter_slaves(self, slaves):
        "Remove slaves that are in an ODOWN or SDOWN state"
        slaves_alive = []
        for slave in slaves:
            if slave["is_odown"] or slave["is_sdown"]:
                continue
            slaves_alive.append((slave["ip"], slave["port"]))
        return slaves_alive

    def discover_slaves(self, service_name):
        "Returns a list of alive slaves for service ``service_name``"
        for sentinel in self.sentinels:
            try:
                slaves = sentinel.sentinel_slaves(service_name)
            except (ConnectionError, ResponseError, TimeoutError):
                continue
            slaves = self.filter_slaves(slaves)
            if slaves:
                return slaves
        return []

    def master_for(
        self,
        service_name,
        redis_class=Redis,
        connection_pool_class=SentinelConnectionPool,
        **kwargs,
    ):
        """
        Returns a redis client instance for the ``service_name`` master.

        A :py:class:`~redis.sentinel.SentinelConnectionPool` class is
        used to retrieve the master's address before establishing a new
        connection.

        NOTE: If the master's address has changed, any cached connections to
        the old master are closed.

        By default clients will be a :py:class:`~redis.Redis` instance.
        Specify a different class to the ``redis_class`` argument if you
        desire something different.

        The ``connection_pool_class`` specifies the connection pool to
        use.  The :py:class:`~redis.sentinel.SentinelConnectionPool`
        will be used by default.

        All other keyword arguments are merged with any connection_kwargs
        passed to this class and passed to the connection pool as keyword
        arguments to be used to initialize Redis connections.
        """
        kwargs["is_master"] = True
        connection_kwargs = dict(self.connection_kwargs)
        connection_kwargs.update(kwargs)
        return redis_class(
            connection_pool=connection_pool_class(
                service_name, self, **connection_kwargs
            )
        )

    def slave_for(
        self,
        service_name,
        redis_class=Redis,
        connection_pool_class=SentinelConnectionPool,
        **kwargs,
    ):
        """
        Returns redis client instance for the ``service_name`` slave(s).

        A SentinelConnectionPool class is used to retrieve the slave's
        address before establishing a new connection.

        By default clients will be a :py:class:`~redis.Redis` instance.
        Specify a different class to the ``redis_class`` argument if you
        desire something different.

        The ``connection_pool_class`` specifies the connection pool to use.
        The SentinelConnectionPool will be used by default.

        All other keyword arguments are merged with any connection_kwargs
        passed to this class and passed to the connection pool as keyword
        arguments to be used to initialize Redis connections.
        """
        kwargs["is_master"] = False
        connection_kwargs = dict(self.connection_kwargs)
        connection_kwargs.update(kwargs)
        return redis_class(
            connection_pool=connection_pool_class(
                service_name, self, **connection_kwargs
            )
        )