Patroni configuration¶
There are 3 types of Patroni configuration:
- Global dynamic configuration.
These options are stored in the DCS (Distributed Configuration Store) and applied on all cluster nodes. Dynamic configuration can be set at any time using
patronictl edit-config
tool or Patroni REST API. If the options changed are not part of the startup configuration, they are applied asynchronously (upon the next wake up cycle) to every node, which gets subsequently reloaded. If the node requires a restart to apply the configuration (for PostgreSQL parameters with context postmaster, if their values have changed), a special flagpending_restart
indicating this is set in the members.data JSON. Additionally, the node status indicates this by showing"restart_pending": true
.
- Local configuration file (patroni.yml).
These options are defined in the configuration file and take precedence over dynamic configuration.
patroni.yml
can be changed and reloaded at runtime (without restart of Patroni) by sending SIGHUP to the Patroni process, performingPOST /reload
REST-API request or executingpatronictl reload
. Local configuration can be either a single YAML file or a directory. When it is a directory, all YAML files in that directory are loaded one by one in sorted order. In case a key is defined in multiple files, the occurrence in the last file takes precedence.
- Environment configuration.
It is possible to set/override some of the “Local” configuration parameters with environment variables. Environment configuration is very useful when you are running in a dynamic environment and you don’t know some of the parameters in advance (for example it’s not possible to know your external IP address when you are running inside
docker
).
Important rules¶
PostgreSQL parameters controlled by Patroni¶
Some of the PostgreSQL parameters must hold the same values on the primary and the replicas. For those, values set either in the local patroni configuration files or via the environment variables take no effect. To alter or set their values one must change the shared configuration in the DCS. Below is the actual list of such parameters together with the default values:
max_connections: 100
max_locks_per_transaction: 64
max_worker_processes: 8
max_prepared_transactions: 0
wal_level: hot_standby
wal_log_hints: on
track_commit_timestamp: off
For the parameters below, PostgreSQL does not require equal values among the primary and all the replicas. However, considering the possibility of a replica to become the primary at any time, it doesn’t really make sense to set them differently; therefore, Patroni restricts setting their values to the dynamic configuration.
max_wal_senders: 5
max_replication_slots: 5
wal_keep_segments: 8
wal_keep_size: 128MB
These parameters are validated to ensure they are sane, or meet a minimum value.
There are some other Postgres parameters controlled by Patroni:
listen_addresses - is set either from
postgresql.listen
or fromPATRONI_POSTGRESQL_LISTEN
environment variableport - is set either from
postgresql.listen
or fromPATRONI_POSTGRESQL_LISTEN
environment variablecluster_name - is set either from
scope
or fromPATRONI_SCOPE
environment variablehot_standby: on
To be on the safe side parameters from the above lists are not written into postgresql.conf
, but passed as a list of arguments to the pg_ctl start
which gives them the highest precedence, even above ALTER SYSTEM
There also are some parameters like postgresql.listen, postgresql.data_dir that can be set only locally, i.e. in the Patroni config file or via configuration variable. In most cases the local configuration will override the dynamic configuration.
When applying the local or dynamic configuration options, the following actions are taken:
The node first checks if there is a postgresql.base.conf or if the
custom_conf
parameter is set.If the
custom_conf
parameter is set, it will take the file specified on it as a base configuration, ignoring postgresql.base.conf and postgresql.conf.If the
custom_conf
parameter is not set and postgresql.base.conf exists, it contains the renamed “original” configuration and it will be used as a base configuration.If there is no
custom_conf`
nor postgresql.base.conf, the original postgresql.conf` is taken and renamed to postgresql.base.conf.The dynamic options (with the exceptions above) are dumped into the postgresql.conf` and an include is set in postgresql.conf to the used base configuration (either postgresql.base.conf or what is on
custom_conf
). Therefore, we would be able to apply new options without re-reading the configuration file to check if the include is present not.Some parameters that are essential for Patroni to manage the cluster are overridden using the command line.
If some of the options that require restart are changed (we should look at the context in pg_settings and at the actual values of those options), a pending_restart flag of a given node is set. This flag is reset on any restart.
The parameters would be applied in the following order (run-time are given the highest priority):
load parameters from file postgresql.base.conf (or from a
custom_conf
file, if set)load parameters from file postgresql.conf
load parameters from file postgresql.auto.conf
run-time parameter using -o –name=value
This allows configuration for all the nodes (2), configuration for a specific node using ALTER SYSTEM
(3) and ensures that parameters essential to the running of Patroni are enforced (4), as well as leaves room for configuration tools that manage postgresql.conf directly without involving Patroni (1).
Patroni configuration parameters¶
Also the following Patroni configuration options can be changed only dynamically:
ttl: 30
loop_wait: 10
retry_timeouts: 10
maximum_lag_on_failover: 1048576
max_timelines_history: 0
check_timeline: false
postgresql.use_slots: true
Upon changing these options, Patroni will read the relevant section of the configuration stored in DCS and change its run-time values.
Patroni nodes are dumping the state of the DCS options to disk upon for every change of the configuration into the file patroni.dynamic.json
located in the Postgres data directory. Only the leader is allowed to restore these options from the on-disk dump if these are completely absent from the DCS or if they are invalid.