patroni.dcs.zookeeper module

class patroni.dcs.zookeeper.PatroniKazooClient(hosts='127.0.0.1:2181', timeout=10.0, client_id=None, handler=None, default_acl=None, auth_data=None, sasl_options=None, read_only=None, randomize_hosts=True, connection_retry=None, command_retry=None, logger=None, keyfile=None, keyfile_password=None, certfile=None, ca=None, use_ssl=False, verify_certs=True, **kwargs)

Bases: kazoo.client.KazooClient

_call(request: Tuple[Any], async_object: kazoo.handlers.threading.AsyncResult) → Optional[bool]

Ensure the client is in CONNECTED or SUSPENDED state and put the request in the queue if it is.

Returns False if the call short circuits due to AUTH_FAILED, CLOSED, or EXPIRED_SESSION state.

class patroni.dcs.zookeeper.PatroniSequentialThreadingHandler(connect_timeout: Union[int, float])

Bases: kazoo.handlers.threading.SequentialThreadingHandler

__init__(connect_timeout: Union[int, float]) → None

Create a SequentialThreadingHandler instance

create_connection(*args: Any, **kwargs: Any) → socket.socket

This method is trying to establish connection with one of the zookeeper nodes.

Somehow strategy “fail earlier and retry more often” works way better comparing to the original strategy “try to connect with specified timeout”. Since we want to try connect to zookeeper more often (with the smaller connect_timeout), he have to override create_connection method in the SequentialThreadingHandler class (which is used by kazoo.Client).

Parameters

args – always contains tuple(host, port) as the first element and could contain connect_timeout (negotiated session timeout) as the second element.

select(*args: Any, **kwargs: Any) → Any

Python 3.XY may raise following exceptions if select/poll are called with an invalid socket: - ValueError: because fd == -1 - TypeError: Invalid file descriptor: -1 (starting from kazoo 2.9) Python 2.7 may raise the IOError instead of socket.error (starting from kazoo 2.9)

When it is appropriate we map these exceptions to socket.error.

set_connect_timeout(connect_timeout: Union[int, float]) → None

class patroni.dcs.zookeeper.ZooKeeper(config: Dict[str, Any], mpp: patroni.postgresql.mpp.AbstractMPP)

Bases: patroni.dcs.AbstractDCS

__init__(config: Dict[str, Any], mpp: patroni.postgresql.mpp.AbstractMPP) → None

Prepare DCS paths, MPP object, initial values for state information and processing dependencies.

Parameters

• config – dict, reference to config section of selected DCS. i.e.: zookeeper for zookeeper, etcd for etcd, etc…

• mpp – an object implementing AbstractMPP interface.

_abc_impl = <_abc._abc_data object>

_cancel_initialization() → None

_create(path: str, value: bytes, retry: bool = False, ephemeral: bool = False) → bool

_delete_leader(leader: patroni.dcs.Leader) → bool

Remove leader key from DCS.

This method should remove leader key if current instance is the leader.

Parameters

leader – Leader object with information about the leader.

Returns

True if successfully committed to DCS.

_kazoo_connect(*args: Any) → Tuple[Union[int, float], Union[int, float]]

Kazoo is using Ping’s to determine health of connection to zookeeper. If there is no response on Ping after Ping interval (1/2 from read_timeout) it will consider current connection dead and try to connect to another node. Without this “magic” it was taking up to 2/3 from session timeout (ttl) to figure out that connection was dead and we had only small time for reconnect and retry.

This method is needed to return different value of read_timeout, which is not calculated from negotiated session timeout but from value of loop_wait. And it is 2 sec smaller than loop_wait, because we can spend up to 2 seconds when calling touch_member() and write_leader_optime() methods, which also may hang…

_load_cluster(path: str, loader: Callable[[str], Union[patroni.dcs.Cluster, Dict[int, patroni.dcs.Cluster]]]) → Union[patroni.dcs.Cluster, Dict[int, patroni.dcs.Cluster]]

Main abstract method that implements the loading of Cluster instance.

Note

Internally this method should call the loader method that will build Cluster object which represents current state and topology of the cluster in DCS. This method supposed to be called only by the get_cluster() method.

Parameters

• path – the path in DCS where to load Cluster(s) from.

• loader – one of _postgresql_cluster_loader() or _mpp_cluster_loader().

Raise

DCSError in case of communication problems with DCS. If the current node was running as a primary and exception raised, instance would be demoted.

_mpp_cluster_loader(path: str) → Dict[int, patroni.dcs.Cluster]

Load and build all PostgreSQL clusters from a single MPP cluster.

Parameters

path – the path in DCS where to load Cluster(s) from.

Returns

all MPP groups as dict, with group IDs as keys and Cluster objects as values.

_postgresql_cluster_loader(path: str) → patroni.dcs.Cluster

Load and build the Cluster object from DCS, which represents a single PostgreSQL cluster.

Parameters

path – the path in DCS where to load Cluster from.

Returns

Cluster instance.

_set_or_create(key: str, value: str, version: Optional[int] = None, retry: bool = False, do_not_create_empty: bool = False) → Union[int, bool]

_update_leader(leader: patroni.dcs.Leader) → bool

Update leader key (or session) ttl.

Note

You have to use CAS (Compare And Swap) operation in order to update leader key, for example for etcd prevValue parameter must be used.

If update fails due to DCS not being accessible or because it is not able to process requests (hopefully temporary), the DCSError exception should be raised.

Parameters

leader – a reference to a current leader object.

Returns

True if leader key (or session) has been updated successfully.

_watcher(event: kazoo.protocol.states.WatchedEvent) → None

_write_failsafe(value: str) → bool

Write current cluster topology to DCS that will be used by failsafe mechanism (if enabled).

Parameters

value – failsafe topology serialized in JSON format.

Returns

True if successfully committed to DCS.

_write_leader_optime(last_lsn: str) → bool

Write current WAL LSN into /optime/leader key in DCS.

Parameters

last_lsn – absolute WAL LSN in bytes.

Returns

True if successfully committed to DCS.

_write_status(value: str) → bool

Write current WAL LSN and confirmed_flush_lsn of permanent slots into the /status key in DCS.

Parameters

value – status serialized in JSON format.

Returns

True if successfully committed to DCS.

attempt_to_acquire_leader() → bool

Attempt to acquire leader lock.

Note

This method should create /leader key with the value _name.

The key must be created atomically. In case the key already exists it should not be overwritten and False must be returned.

If key creation fails due to DCS not being accessible or because it is not able to process requests (hopefully temporary), the DCSError exception should be raised.

Returns

True if key has been created successfully.

cancel_initialization() → bool

Removes the initialize key for a cluster.

Returns

True if successfully committed to DCS.

delete_cluster() → bool

Delete cluster from DCS.

Returns

True if successfully committed to DCS.

delete_sync_state(version: Optional[int] = None) → bool

Delete the synchronous state from DCS.

Parameters

version – for conditional deletion of the key/object.

Returns

True if delete successful.

get_children(key: str) → List[str]

get_node(key: str, watch: Optional[Callable[[kazoo.protocol.states.WatchedEvent], None]] = None) → Optional[Tuple[str, kazoo.protocol.states.ZnodeStat]]

get_status(path: str, leader: Optional[patroni.dcs.Leader]) → patroni.dcs.Status

initialize(create_new: bool = True, sysid: str = '') → bool

Race for cluster initialization.

This method should atomically create initialize key and return True, otherwise it should return False.

Parameters

• create_new – False if the key should already exist (in the case we are setting the system_id).

• sysid – PostgreSQL cluster system identifier, if specified, is written to the key.

Returns

True if key has been created successfully.

load_members(path: str) → List[patroni.dcs.Member]

static member(name: str, value: str, znode: kazoo.protocol.states.ZnodeStat) → patroni.dcs.Member

reload_config(config: Union[Config, Dict[str, Any]]) → None

Load and set relevant values from configuration.

Sets loop_wait, ttl and retry_timeout properties.

Parameters

config – Loaded configuration information object or dictionary of key value pairs.

set_config_value(value: str, version: Optional[int] = None) → bool

Create or update /config key in DCS.

Parameters

• value – new value to set in the config key.

• version – for conditional update of the key/object.

Returns

True if successfully committed to DCS.

set_failover_value(value: str, version: Optional[int] = None) → bool

Create or update /failover key.

Parameters

• value – value to set.

• version – for conditional update of the key/object.

Returns

True if successfully committed to DCS.

set_history_value(value: str) → bool

Set value for history in DCS.

Parameters

value – new value of history key/object.

Returns

True if successfully committed to DCS.

set_retry_timeout(retry_timeout: int) → None

Set the new value for retry_timeout.

set_sync_state_value(value: str, version: Optional[int] = None) → Union[int, bool]

Set synchronous state in DCS.

Parameters

• value – the new value of /sync key.

• version – for conditional update of the key/object.

Returns

version of the new object or False in case of error.

set_ttl(ttl: int) → Optional[bool]

It is not possible to change ttl (session_timeout) in zookeeper without destroying old session and creating the new one. This method returns !True if session_timeout has been changed (restart() has been called).

take_leader() → bool

Establish a new leader in DCS.

Note

This method should create leader key with value of _name and ttl of ttl.

Since it could be called only on initial cluster bootstrap it could create this key regardless, overwriting the key if necessary.

Returns

True if successfully committed to DCS.

touch_member(data: Dict[str, Any]) → bool

Update member key in DCS.

Note

This method should create or update key with the name with /members/ + _name and the value of data in a given DCS.

Parameters

data – information about an instance (including connection strings).

Returns

True if successfully committed to DCS.

property ttl: int

Get current ttl value.

watch(leader_version: Optional[int], timeout: float) → bool

Sleep if the current node is a leader, otherwise, watch for changes of leader key with a given timeout.

Parameters

• leader_version – version of a leader key.

• timeout – timeout in seconds.

Returns

if True this will reschedule the next run of the HA cycle.

exception patroni.dcs.zookeeper.ZooKeeperError(value: Any)

Bases: patroni.exceptions.DCSError