Originally we were passing postgresql options as an argument of `pg_ctl
start`. It was nice and convenient because doesn't require to touch
configuration files but this method has one significant drawback: it
wasn't possible to change values of options which were passed as an
arguments without restart (event for the case when option reqires only
reload). Instead of doing that (passing options as arguments) we will:
1) rename original postgresql.conf to postgresql-base.conf
2) write options into postgresql.conf which has `include
'postgresql-base.conf'` on the the third line after comment that this
file is generated by Patroni and you should not change it manually
3) listen_addresses and port are still passed as an arguments to the
pg_ctl (just to be foolproof against ALTER SYSTEM set port to 'random')
In addition to that this commit makes some attributes of `Postgresql`
class private (prefixes them with _)
Mostly this tag is necessary to give a hint to load balancer
auto-configuration tool that node should not be included into
LB configuration.
In addition to that Patroni also should not return status_code=200
for a health check if the tag is present and value is not `False`.
Until now get_dcs method was doing absolutely the same job as method
from Patroni class.
In addition to that I did small refactoring and clean up of unit tests
In addition to that rename confusing `Etcd.client` and
`ZooKeeper.client` into `_client`. This attribute is available from
AbstractDCS and people had wrong impression that it provides the same
interface for different DCS implementations, which is obviously not the
case. For Etcd it has type etcd.Client and for ZooKeeper - KazooClient.
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.
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.
First time is triggers some shutdown mechanisms in a patroni, but the
second one just terminates patroni. Solution is pretty simple, we need
to ignore all other sigterms which are coming after the first one.
Current etcd implementation does not yet support timeout option when
`wait=true`: https://github.com/coreos/etcd/issues/2468
Originaly I've implemented `watch` method for `Etcd` class in a
following manner: if the leader key was updated just because master
needs to update ttl and watch timeout is not yet expired, I was
recalculating timeout and starting `watch` call once again.
Usually after "restart" we were getting urllib3.exceptions.TimeoutError.
The only possible way to recover after such exception - close socket and
establish a new connection. With pure http it's relatively cheap, but
with https and some kind of authorization on etcd side it would became
rather expensive and should be avoided.
user:passwd pair should be configured in restapi section of main
configuration file in following format:
restapi:
auth: 'username:password'
Plus implemented some simple routing mechanisms:
GET /foo => do_GET_foo()
POST /bar => do_POST_bar()
Cleanup the initialize flag if the initializing node fails
to bootstrap its PostgreSQL database.
Rename dcs.race to initialize, since we only call it for the
initialize flag. Factored out PostgreSQL bootstrapping code
into a separate function.
`Cluster.leader` is not reference to `Member` anymore, but to `Leader`
`Leader` class contains field `index` (update index). This field is very
useful for watching for events which changing leader key. Also `Leader`
contains `member` field, which should reference real member.
Alexander Kukushkin