Patroni

Patroni REST API

Patroni has a rich REST API, which is used by Patroni itself during the leader race, by the patronictl tool in order to perform failovers/switchovers/reinitialize/restarts/reloads, by HAProxy or any other kind of load balancer to perform HTTP health checks, and of course could also be used for monitoring. Below you will find the list of Patroni REST API endpoints.

Health check endpoints

For all health check GET requests Patroni returns a JSON document with the status of the node, along with the HTTP status code. If you don’t want or don’t need the JSON document, you might consider using the HEAD or OPTIONS method instead of GET.

  • The following requests to Patroni REST API will return HTTP status code 200 only when the Patroni node is running as the primary with leader lock:

  • GET`+ ``/standby-leader+`: returns HTTP status code 200 only when the Patroni node is running as the leader in a standby cluster.

  • GET`+ ``/leader+: returns HTTP status code 200 when the Patroni node has the leader lock. The major difference from the two previous endpoints is that it doesn’t take into account whether PostgreSQL is running as the `+primary+ or the standby_leader.

  • GET`+ ``/replica+: replica health check endpoint. It returns HTTP status code 200 only when the Patroni node is in the state `+running+, the role is replica and noloadbalance tag is not set.

  • GET`+ ``/replica?lag=<max-lag>`: replica check endpoint. In addition to checks from `+replica`, it also checks replication latency and returns status code 200 only when it is below specified value. The key cluster.last_leader_operation from DCS is used for Leader wal position and compute latency on replica for performance reasons. max-lag can be specified in bytes (integer) or in human readable values, for e.g. 16kB, 64MB, 1GB.

  • GET`+ ``/replica?tag_key1=value1&tag_key2=value2+: replica check endpoint. In addition, It will also check for user defined tags `+key1+ and key2 and their respective values in the tags section of the yaml configuration management. If the tag isn’t defined for an instance, or if the value in the yaml configuration doesn’t match the querying value, it will return HTTP Status Code 503.

    In the following requests, since we are checking for the leader or standby-leader status, Patroni doesn’t apply any of the user defined tags and they will be ignored.

  • GET`+ ``/read-only+`: like the above endpoint, but also includes the primary.

  • GET+ ``/synchronous+ or GET+ ``/sync+: returns HTTP status code 200 only when the Patroni node is running as a synchronous standby.

  • GET`+ ``/read-only-sync+`: like the above endpoint, but also includes the primary.

  • GET+ ``/asynchronous+ or GET+ ``/async+: returns HTTP status code 200 only when the Patroni node is running as an asynchronous standby.

  • GET+ ``/asynchronous?lag=<max-lag>` or `+GET+ +`/async?lag=<max-lag>: asynchronous standby check endpoint. In addition to checks from `asynchronous or async, it also checks replication latency and returns status code 200 only when it is below specified value. The key cluster.last_leader_operation from DCS is used for Leader wal position and compute latency on replica for performance reasons. max-lag can be specified in bytes (integer) or in human readable values, for e.g. 16kB, 64MB, 1GB.

  • GET`+ ``/health+`: returns HTTP status code 200 only when PostgreSQL is up and running.

  • GET`+ ``/liveness+: returns HTTP status code 200 if Patroni heartbeat loop is properly running and 503 if the last run was more than `+ttl+ seconds ago on the primary or 2*ttl on the replica. Could be used for livenessProbe.

  • GET`+ ``/readiness+: returns HTTP status code 200 when the Patroni node is running as the leader or when PostgreSQL is up and running. The endpoint could be used for `+readinessProbe+ when it is not possible to use Kubernetes endpoints for leader elections (OpenShift).

Both, readiness and liveness endpoints are very light-weight and not executing any SQL. Probes should be configured in such a way that they start failing about time when the leader key is expiring. With the default value of ttl, which is 30s example probes would look like:

readinessProbe:
   httpGet:
    scheme: HTTP
    path: /readiness
    port: 8008
  initialDelaySeconds: 3
  periodSeconds: 10
  timeoutSeconds: 5
  successThreshold: 1
  failureThreshold: 3
livenessProbe:
   httpGet:
    scheme: HTTP
    path: /liveness
    port: 8008
  initialDelaySeconds: 3
  periodSeconds: 10
  timeoutSeconds: 5
  successThreshold: 1
  failureThreshold: 3

Monitoring endpoint

The GET`+ ``/patroni+` is used by Patroni during the leader race. It also could be used by your monitoring system. The JSON document produced by this endpoint has the same structure as the JSON produced by the health check endpoints.

Example: A healthy cluster

$ curl -s  http://localhost:8008/patroni | jq .
{
  "state": "running",
  "postmaster_start_time": "2023-08-18 11:03:37.966359+00:00",
  "role": "master",
  "server_version": 150004,
  "xlog": {
    "location": 67395656
  },
  "timeline": 1,
  "replication": [
    {
      "usename": "replicator",
      "application_name": "patroni2",
      "client_addr": "10.89.0.6",
      "state": "streaming",
      "sync_state": "async",
      "sync_priority": 0
    },
    {
      "usename": "replicator",
      "application_name": "patroni3",
      "client_addr": "10.89.0.2",
      "state": "streaming",
      "sync_state": "async",
      "sync_priority": 0
    }
  ],
  "dcs_last_seen": 1692356718,
  "tags": {
    "clonefrom": true
  },
  "database_system_identifier": "7268616322854375442",
  "patroni": {
    "version": "3.1.0",
    "scope": "demo",
    "name": "patroni1"
  }
}

Example: An unlocked cluster

$ curl -s  http://localhost:8008/patroni  | jq .
{
  "state": "running",
  "postmaster_start_time": "2023-08-18 11:09:08.615242+00:00",
  "role": "replica",
  "server_version": 150004,
  "xlog": {
    "received_location": 67419744,
    "replayed_location": 67419744,
    "replayed_timestamp": null,
    "paused": false
  },
  "timeline": 1,
  "replication": [
    {
      "usename": "replicator",
      "application_name": "patroni2",
      "client_addr": "10.89.0.6",
      "state": "streaming",
      "sync_state": "async",
      "sync_priority": 0
    },
    {
      "usename": "replicator",
      "application_name": "patroni3",
      "client_addr": "10.89.0.2",
      "state": "streaming",
      "sync_state": "async",
      "sync_priority": 0
    }
  ],
  "cluster_unlocked": true,
  "dcs_last_seen": 1692356928,
  "tags": {
    "clonefrom": true
  },
  "database_system_identifier": "7268616322854375442",
  "patroni": {
    "version": "3.1.0",
    "scope": "demo",
    "name": "patroni1"
  }
}

Example: An unlocked cluster with DCS failsafe mode enabled

$ curl -s  http://localhost:8008/patroni  | jq .
{
  "state": "running",
  "postmaster_start_time": "2023-08-18 11:09:08.615242+00:00",
  "role": "replica",
  "server_version": 150004,
  "xlog": {
    "location": 67420024
  },
  "timeline": 1,
  "replication": [
    {
      "usename": "replicator",
      "application_name": "patroni2",
      "client_addr": "10.89.0.6",
      "state": "streaming",
      "sync_state": "async",
      "sync_priority": 0
    },
    {
      "usename": "replicator",
      "application_name": "patroni3",
      "client_addr": "10.89.0.2",
      "state": "streaming",
      "sync_state": "async",
      "sync_priority": 0
    }
  ],
  "cluster_unlocked": true,
  "failsafe_mode_is_active": true,
  "dcs_last_seen": 1692356928,
  "tags": {
    "clonefrom": true
  },
  "database_system_identifier": "7268616322854375442",
  "patroni": {
    "version": "3.1.0",
    "scope": "demo",
    "name": "patroni1"
  }
}

Example: A cluster with the pause mode enabled

$ curl -s  http://localhost:8008/patroni  | jq .
{
  "state": "running",
  "postmaster_start_time": "2023-08-18 11:09:08.615242+00:00",
  "role": "replica",
  "server_version": 150004,
  "xlog": {
    "location": 67420024
  },
  "timeline": 1,
  "replication": [
    {
      "usename": "replicator",
      "application_name": "patroni2",
      "client_addr": "10.89.0.6",
      "state": "streaming",
      "sync_state": "async",
      "sync_priority": 0
    },
    {
      "usename": "replicator",
      "application_name": "patroni3",
      "client_addr": "10.89.0.2",
      "state": "streaming",
      "sync_state": "async",
      "sync_priority": 0
    }
  ],
  "pause": true,
  "dcs_last_seen": 1692356928,
  "tags": {
    "clonefrom": true
  },
  "database_system_identifier": "7268616322854375442",
  "patroni": {
    "version": "3.1.0",
    "scope": "demo",
    "name": "patroni1"
  }
}

Retrieve the Patroni metrics in Prometheus format through the GET`+ ``/metrics+` endpoint.

$ curl  http://localhost:8008/metrics

# HELP patroni_version Patroni semver without periods. \
# TYPE patroni_version gauge
patroni_version{scope="batman",name="patroni1"} 020103
# HELP patroni_postgres_running Value is 1 if Postgres is running, 0 otherwise.
# TYPE patroni_postgres_running gauge
patroni_postgres_running{scope="batman",name="patroni1"} 1
# HELP patroni_postmaster_start_time Epoch seconds since Postgres started.
# TYPE patroni_postmaster_start_time gauge
patroni_postmaster_start_time{scope="batman",name="patroni1"} 1657656955.179243
# HELP patroni_master Value is 1 if this node is the leader, 0 otherwise.
# TYPE patroni_master gauge
patroni_master{scope="batman",name="patroni1"} 1
# HELP patroni_primary Value is 1 if this node is the leader, 0 otherwise.
# TYPE patroni_primary gauge
patroni_primary{scope="batman",name="patroni1"} 1
# HELP patroni_xlog_location Current location of the Postgres transaction log, 0 if this node is not the leader.
# TYPE patroni_xlog_location counter
patroni_xlog_location{scope="batman",name="patroni1"} 22320573386952
# HELP patroni_standby_leader Value is 1 if this node is the standby_leader, 0 otherwise.
# TYPE patroni_standby_leader gauge
patroni_standby_leader{scope="batman",name="patroni1"} 0
# HELP patroni_replica Value is 1 if this node is a replica, 0 otherwise.
# TYPE patroni_replica gauge
patroni_replica{scope="batman",name="patroni1"} 0
# HELP patroni_sync_standby Value is 1 if this node is a sync standby replica, 0 otherwise.
# TYPE patroni_sync_standby gauge
patroni_sync_standby{scope="batman",name="patroni1"} 0
# HELP patroni_xlog_received_location Current location of the received Postgres transaction log, 0 if this node is not a replica.
# TYPE patroni_xlog_received_location counter
patroni_xlog_received_location{scope="batman",name="patroni1"} 0
# HELP patroni_xlog_replayed_location Current location of the replayed Postgres transaction log, 0 if this node is not a replica.
# TYPE patroni_xlog_replayed_location counter
patroni_xlog_replayed_location{scope="batman",name="patroni1"} 0
# HELP patroni_xlog_replayed_timestamp Current timestamp of the replayed Postgres transaction log, 0 if null.
# TYPE patroni_xlog_replayed_timestamp gauge
patroni_xlog_replayed_timestamp{scope="batman",name="patroni1"} 0
# HELP patroni_xlog_paused Value is 1 if the Postgres xlog is paused, 0 otherwise.
# TYPE patroni_xlog_paused gauge
patroni_xlog_paused{scope="batman",name="patroni1"} 0
# HELP patroni_postgres_streaming Value is 1 if Postgres is streaming, 0 otherwise.
# TYPE patroni_postgres_streaming gauge
patroni_postgres_streaming{scope="batman",name="patroni1"} 1
# HELP patroni_postgres_in_archive_recovery Value is 1 if Postgres is replicating from archive, 0 otherwise.
# TYPE patroni_postgres_in_archive_recovery gauge
patroni_postgres_in_archive_recovery{scope="batman",name="patroni1"} 0
# HELP patroni_postgres_server_version Version of Postgres (if running), 0 otherwise.
# TYPE patroni_postgres_server_version gauge
patroni_postgres_server_version{scope="batman",name="patroni1"} 140004
# HELP patroni_cluster_unlocked Value is 1 if the cluster is unlocked, 0 if locked.
# TYPE patroni_cluster_unlocked gauge
patroni_cluster_unlocked{scope="batman",name="patroni1"} 0
# HELP patroni_postgres_timeline Postgres timeline of this node (if running), 0 otherwise.
# TYPE patroni_postgres_timeline counter
patroni_failsafe_mode_is_active{scope="batman",name="patroni1"} 0
# HELP patroni_postgres_timeline Postgres timeline of this node (if running), 0 otherwise.
# TYPE patroni_postgres_timeline counter
patroni_postgres_timeline{scope="batman",name="patroni1"} 24
# HELP patroni_dcs_last_seen Epoch timestamp when DCS was last contacted successfully by Patroni.
# TYPE patroni_dcs_last_seen gauge
patroni_dcs_last_seen{scope="batman",name="patroni1"} 1677658321
# HELP patroni_pending_restart Value is 1 if the node needs a restart, 0 otherwise.
# TYPE patroni_pending_restart gauge
patroni_pending_restart{scope="batman",name="patroni1"} 1
# HELP patroni_is_paused Value is 1 if auto failover is disabled, 0 otherwise.
# TYPE patroni_is_paused gauge
patroni_is_paused{scope="batman",name="patroni1"} 1

Cluster status endpoints

$ curl -s  http://localhost:8008/cluster | jq .
{
  "members": [
    {
      "name": "patroni1",
      "role": "leader",
      "state": "running",
      "api_url": " http://10.89.0.4:8008/patroni",
      "host": "10.89.0.4",
      "port": 5432,
      "timeline": 5,
      "tags": {
        "clonefrom": true
      }
    },
    {
      "name": "patroni2",
      "role": "replica",
      "state": "streaming",
      "api_url": " http://10.89.0.6:8008/patroni",
      "host": "10.89.0.6",
      "port": 5433,
      "timeline": 5,
      "tags": {
        "clonefrom": true
      },
      "lag": 0
    }
  ],
  "scope": "demo",
  "scheduled_switchover": {
    "at": "2023-09-24T10:36:00+02:00",
    "from": "patroni1",
    "to": "patroni3"
  }
}
$ curl -s  http://localhost:8008/history | jq .
[
  [
    1,
    25623960,
    "no recovery target specified",
    "2019-09-23T16:57:57+02:00"
  ],
  [
    2,
    25624344,
    "no recovery target specified",
    "2019-09-24T09:22:33+02:00"
  ],
  [
    3,
    25624752,
    "no recovery target specified",
    "2019-09-24T09:26:15+02:00"
  ],
  [
    4,
    50331856,
    "no recovery target specified",
    "2019-09-24T09:35:52+02:00"
  ]
]

Config endpoint

GET`+ ``/config+`: Get the current version of the dynamic configuration:

$ curl -s  http://localhost:8008/config | jq .
{
  "ttl": 30,
  "loop_wait": 10,
  "retry_timeout": 10,
  "maximum_lag_on_failover": 1048576,
  "postgresql": {
    "use_slots": true,
    "use_pg_rewind": true,
    "parameters": {
      "hot_standby": "on",
      "wal_level": "hot_standby",
      "max_wal_senders": 5,
      "max_replication_slots": 5,
      "max_connections": "100"
    }
  }
}

PATCH`+ ``/config+`: Change the existing configuration.

$ curl -s -XPATCH -d \
        '{"loop_wait":5,"ttl":20,"postgresql":{"parameters":{"max_connections":"101"}}}' \
         http://localhost:8008/config | jq .
{
  "ttl": 20,
  "loop_wait": 5,
  "maximum_lag_on_failover": 1048576,
  "retry_timeout": 10,
  "postgresql": {
    "use_slots": true,
    "use_pg_rewind": true,
    "parameters": {
      "hot_standby": "on",
      "wal_level": "hot_standby",
      "max_wal_senders": 5,
      "max_replication_slots": 5,
      "max_connections": "101"
    }
  }
}

The above REST API call patches the existing configuration and returns the new configuration.

Let’s check that the node processed this configuration. First of all it should start printing log lines every 5 seconds (loop_wait=5). The change of “max_connections” requires a restart, so the “pending_restart” flag should be exposed:

$ curl -s  http://localhost:8008/patroni | jq .
{
  "pending_restart": true,
  "database_system_identifier": "6287881213849985952",
  "postmaster_start_time": "2016-06-13 13:13:05.211 CEST",
  "xlog": {
    "location": 2197818976
  },
  "patroni": {
    "version": "1.0",
    "scope": "batman",
    "name": "patroni1"
  },
  "state": "running",
  "role": "master",
  "server_version": 90503
}

Removing parameters:

If you want to remove (reset) some setting just patch it with null:

$ curl -s -XPATCH -d \
        '{"postgresql":{"parameters":{"max_connections":null}}}' \
         http://localhost:8008/config | jq .
{
  "ttl": 20,
  "loop_wait": 5,
  "retry_timeout": 10,
  "maximum_lag_on_failover": 1048576,
  "postgresql": {
    "use_slots": true,
    "use_pg_rewind": true,
    "parameters": {
      "hot_standby": "on",
      "unix_socket_directories": ".",
      "wal_level": "hot_standby",
      "max_wal_senders": 5,
      "max_replication_slots": 5
    }
  }
}

The above call removes postgresql.parameters.max_connections from the dynamic configuration.

PUT`+ ``/config+`: It’s also possible to perform the full rewrite of an existing dynamic configuration unconditionally:

$ curl -s -XPUT -d \
        '{"maximum_lag_on_failover":1048576,"retry_timeout":10,"postgresql":{"use_slots":true,"use_pg_rewind":true,"parameters":{"hot_standby":"on","wal_level":"hot_standby","unix_socket_directories":".","max_wal_senders":5}},"loop_wait":3,"ttl":20}' \
         http://localhost:8008/config | jq .
{
  "ttl": 20,
  "maximum_lag_on_failover": 1048576,
  "retry_timeout": 10,
  "postgresql": {
    "use_slots": true,
    "parameters": {
      "hot_standby": "on",
      "unix_socket_directories": ".",
      "wal_level": "hot_standby",
      "max_wal_senders": 5
    },
    "use_pg_rewind": true
  },
  "loop_wait": 3
}

Switchover and failover endpoints

Switchover

/switchover endpoint only works when the cluster is healthy (there is a leader). It also allows to schedule a switchover at a given time.

When calling /switchover endpoint a candidate can be specified but is not required, in contrast to /failover endpoint. If a candidate is not provided, all the eligible nodes of the cluster will participate in the leader race after the leader stepped down.

In the JSON body of the POST request you must specify the leader field. The candidate and the scheduled_at fields are optional and can be used to schedule a switchover at a specific time.

Depending on the situation, requests might return different HTTP status codes and bodies. Status code 200 is returned when the switchover or failover successfully completed. If the switchover was successfully scheduled, Patroni will return HTTP status code 202. In case something went wrong, the error status code (one of 400, 412, or 503) will be returned with some details in the response body.

DELETE`+ ``/switchover+` can be used to delete the currently scheduled switchover.

Example: perform a switchover to any healthy standby

$ curl -s  http://localhost:8008/switchover -XPOST -d '{"leader":"postgresql1"}'
Successfully switched over to "postgresql2"

Example: perform a switchover to a specific node

$ curl -s  http://localhost:8008/switchover -XPOST -d \
        '{"leader":"postgresql1","candidate":"postgresql2"}'
Successfully switched over to "postgresql2"

Example: schedule a switchover from the leader to any other healthy standby in the cluster at a specific time.

$ curl -s  http://localhost:8008/switchover -XPOST -d \
        '{"leader":"postgresql0","scheduled_at":"2019-09-24T12:00+00"}'
Switchover scheduled

Failover

/failover endpoint can be used to perform a manual failover when there are no healthy nodes (e.g. to an asynchronous standby if all synchronous standbys are not healthy enough to promote). However there is no requirement for a cluster not to have leader - failover can also be run on a healthy cluster.

In the JSON body of the POST request you must specify the candidate field. If the leader field is specified, a switchover is triggered instead.

Example:

$ curl -s  http://localhost:8008/failover -XPOST -d '{"candidate":"postgresql1"}'
Successfully failed over to "postgresql1"

Warning

Be very careful when using this endpoint, as this can cause data loss in certain situations. In most cases, the switchover endpoint satisfies the administrator’s needs.

POST+ ``/switchover+ and POST+ ``/failover+ endpoints are used by patronictl switchover and patronictl failover, respectively.

DELETE`+ ``/switchover+` is used by patronictl flush cluster-name switchover.

Failover/Switchover comparison
Failover Switchover

Requires leader specified

no

yes

Requires candidate specified

yes

no

Can be run in pause

yes

yes (only to a specific candidate)

Can be scheduled

no

yes (if not in pause)

Healthy standby

There are a couple of checks that a member of a cluster should pass to be able to participate in the leader race during a switchover or to become a leader as a failover/switchover candidate:

Warning

In case of a manual failover in a cluster without a leader, a candidate will be allowed to promote even if

=== Restart endpoint

DELETE`+ ``/restart+`: delete the scheduled restart

POST+ ``/restart+ and DELETE+ ``/restart+ endpoints are used by patronictl restart and patronictl flush cluster-name restart respectively.

Reload endpoint

The POST+ ``/reload+ call will order Patroni to re-read and apply the configuration file. This is the equivalent of sending the SIGHUP signal to the Patroni process. In case you changed some of the Postgres parameters which require a restart (like shared_buffers), you still have to explicitly do the restart of Postgres by either calling the POST+ ``/restart+ endpoint or with the help of patronictl restart.

The reload endpoint is used by patronictl reload.

Reinitialize endpoint

POST`+ ``/reinitialize+: reinitialize the PostgreSQL data directory on the specified node. It is allowed to be executed only on replicas. Once called, it will remove the data directory and start `+pg_basebackup+ or some alternative replica creation method.

The call might fail if Patroni is in a loop trying to recover (restart) a failed Postgres. In order to overcome this problem one can specify {"force":true} in the request body.

The reinitialize endpoint is used by patronictl reinit.

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