Previously, the leader key was watched for changes after a failover. This resulted in a delay
of up to 10 seconds to report a healthy failover back to the client.
With this patch, we are not relying on the role of a member registered in the dcs anymore.
For managing Patroni clusters, the Patroni api can be used. For many tasks, a command line interface for
this api would be a useful addition. This commit adds patroncli (The name is still under debate).
The command line interface needs access to the DCS; this is required for any operation. For some tasks it is required
to have access to the Patroni api.
A small summary of the additions to get the cli/ctl started:
* Updated Docker image to use 'true' as the archive_command, to ensure disk not filling up during failover
testing.
* The cli currently can list members, failover a master and remove a given cluster from DCS.
* The cli can be configured with a command, for repeated access to the same DCS
* Added some simple tests for the cli, code coverage is very low
Tags are labels assigned to individual members in order
to alter its default behavior, i.e. exclude from the
leader election or indicate a possibility to create base
backups from the member.
This commit only adds support for setting tags in the
configuration file, exposes the tags to DCS /member subkey
and returns the tags in a response of the API request. At
the moment the tag names are not validated, nor they are
interpreted in any way.
Support for setting tags via the API is also in the scope
of further work.
1. run touch_member from the main loop
2. move code which takes care about long tasks into separate class
3. change format of data stored in a DCS: use json instead of url
4. change Member class: from now it deserialize everything into data property
5. rework API: from now it takes into account state of the current node in a dcs
Implementation is done on top of feature/is-healthiest-via-api and
feature/api branches.
In order to trigger manual failover one has to create 'failover' key in
a configuration store with the value in following format:
'leader_name:member_name'
leader_name can be empty or should match with the name of current leader
member_name can be empty or should match with the name one of cluster
nodes
Leader always checks that either desired member (if specified) or one of
the memners is accessible and healthy before demote.
After leader has deomted himself other nodes are performig checks that
desired node is healthy. If it is not they are participating in a leader
race. In some cases (when accidently there is no healthy nodes) former
leader can also participate in a leader race.
Current implementation does not provide REST API endpoint for a manual
failover.
POST /restart -- will restart postgres
You you are restartung leader node, lock would be maintained during
restart.
POST /reinitialize -- will reinitialize node from the leader.
It's not possible to reinitialize current leader.
Command will fail when the leader is unknown.
query method in an api.py also needs retry in some cases (for example
when we are running is_healthiest_node check).
In all cases we should retry only when connection is closed or broken.
BUT, the connection status must be checked via cursor.connection (old
implementation was using general connection object for that). For
multi-threaded applications this is not appropriate, because some other
thread might restore connection.
In addition to that I've changed most of the unit tests to use `Mock` and
`patch` where it is possible.
In case if one member of a cluster is not available it will retry with
another one and fetch the new cluster configuration. Default timeout for
all requests to etcd is 5 seconds.
Initial cluster configuration can be resolved through:
1) /v2/members call on one of the cluster members on a client port
2) when it is possible to resolve hostname into multiple ip's it will
iterate through list and try to perform action from 1)
3) If there is discovery_srv defined in etcd section of config file it
will resolve peer addresses of all cluster members and will fetch
cluster configuration with using peer protocol by doing /members call on
a peer port
Also check presence of trigger_file on master after promotion when
pg_is_in_recovery() = false and if it is there - remove it.
Plus check presence of trigger_file on a new slave (after running
pg_basebackup) and if it is there - also remove it.
Oleksii Kliukin