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be more permissive with standbys

This commit is contained in:
Felix Kunde 2020-02-24 12:52:05 +01:00
parent 7b94060d17
commit 236fbbf2c6
4 changed files with 82 additions and 30 deletions
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10
docs/administrator.md
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@ -11,11 +11,11 @@ switchover (planned failover) of the master to the Pod with new minor version.
The switch should usually take less than 5 seconds, still clients have to The switch should usually take less than 5 seconds, still clients have to
reconnect. reconnect.
Major version upgrades are supported via [cloning](user.md#clone-directly). The Major version upgrades are supported via [cloning](user.md#how-to-clone-an-existing-postgresql-cluster).
new cluster manifest must have a higher `version` string than the source cluster The new cluster manifest must have a higher `version` string than the source
and will be created from a basebackup. Depending of the cluster size, downtime cluster and will be created from a basebackup. Depending of the cluster size,
in this case can be significant as writes to the database should be stopped and downtime in this case can be significant as writes to the database should be
all WAL files should be archived first before cloning is started. stopped and all WAL files should be archived first before cloning is started.
Note, that simply changing the version string in the `postgresql` manifest does Note, that simply changing the version string in the `postgresql` manifest does
not work at present and leads to errors. Neither Patroni nor Postgres Operator not work at present and leads to errors. Neither Patroni nor Postgres Operator

5
docs/reference/operator_parameters.md
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@ -110,8 +110,9 @@ Those are top-level keys, containing both leaf keys and groups.
* **min_instances** * **min_instances**
operator will run at least the number of instances for any given Postgres operator will run at least the number of instances for any given Postgres
cluster equal to the value of this parameter. When `-1` is specified, no cluster equal to the value of this parameter, except for standby clusters
limits are applied. The default is `-1`. which run with one pod if `numberOfInstances` is set to 1. When `-1` is
specified for `min_instances`, no limits are applied. The default is `-1`.
* **resync_period** * **resync_period**
period between consecutive sync requests. The default is `30m`. period between consecutive sync requests. The default is `30m`.

87
docs/user.md
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@ -317,14 +317,21 @@ spec:
s3_force_path_style: true s3_force_path_style: true
``` ```
Note, that cloning can also be used for [major version upgrades](administrator.md#minor-and-major-version-upgrade)
of PostgreSQL.
## Setting up a standby cluster ## Setting up a standby cluster
Standby clusters are like normal cluster but they are streaming from a remote Standby cluster is a [Patroni feature](https://github.com/zalando/patroni/blob/master/docs/replica_bootstrap.rst#standby-cluster)
cluster. As the first version of this feature, the only scenario covered by that first clones a database, and keeps replicating changes afterwards. As the
operator is to stream from a WAL archive of the master. Following the more replication is happening by the means of archived WAL files (stored on S3 or
popular infrastructure of using Amazon's S3 buckets, it is mentioned as the equivalent of other cloud providers), the standby cluster can exist in a
`s3_wal_path` here. To start a cluster as standby add the following `standby` different location than its source database. Unlike cloning, the PostgreSQL
section in the YAML file: version between source and target cluster has to be the same.
To start a cluster as standby, add the following `standby` section in the YAML
file and specify the S3 bucket path. An empty path will result in an error and
no statefulset will be created.
```yaml ```yaml
spec: spec:
@ -332,20 +339,62 @@ spec:
s3_wal_path: "s3 bucket path to the master" s3_wal_path: "s3 bucket path to the master"
``` ```
Things to note: At the moment, the operator only allows to stream from the WAL archive of the
master. Thus, it is recommended to deploy standby clusters with only [one pod](../manifests/standby-manifest.yaml#L10).
You can raise the instance count when detaching. Note, that the same pod role
labels like for normal clusters are used: The standby leader is labeled as
`master`.
- An empty string in the `s3_wal_path` field of the standby cluster will result ### Providing credentials of source cluster
in an error and no statefulset will be created.
- Only one pod can be deployed for stand-by cluster. A standby cluster is replicating the data (including users and passwords) from
- To manually promote the standby_cluster, use `patronictl` and remove config the source database and is read-only. The system and application users (like
entry. standby, postgres etc.) all have a password that does not match the credentials
- There is no way to transform a non-standby cluster to a standby cluster stored in secrets which are created by the operator. One solution is to create
through the operator. Adding the standby section to the manifest of a running secrets beforehand and paste in the credentials of the source cluster.
Postgres cluster will have no effect. However, it can be done through Patroni Otherwise, you will see errors in the Postgres logs saying users cannot log in
by adding the [standby_cluster](https://github.com/zalando/patroni/blob/bd2c54581abb42a7d3a3da551edf0b8732eefd27/docs/replica_bootstrap.rst#standby-cluster) and the operator logs will complain about not being able to sync resources.
section using `patronictl edit-config`. Note that the transformed standby This, however, can safely be ignored as it will be sorted out once the cluster
cluster will not be doing any streaming. It will be in standby mode and allow is detached from the source (and it’s still harmless if you don’t plan to).
read-only transactions only.
You can also edit the secrets afterwards. Find them by:
```bash
kubectl get secrets --all-namespaces | grep <postgres-cluster-name>
```
### Promote the standby
One big advantage of standby clusters is that they can be promoted to a proper
database cluster. This means it will stop replicating changes from the source,
and start accept writes itself. This mechanism makes it possible to move
databases from one place to another with minimal downtime. Currently, the
operator does not support promoting a standby cluster. It has to be done
manually using `patronictl edit-config` inside the postgres container of the
standby leader pod. Remove the following lines from the YAML structure and the
leader promotion happens immediately. Before doing so, make sure that the
standby is not behind the source database.
```yaml
standby_cluster:
create_replica_methods:
- bootstrap_standby_with_wale
- basebackup_fast_xlog
restore_command: envdir "/home/postgres/etc/wal-e.d/env-standby" /scripts/restore_command.sh
"%f" "%p"
```
Finally, remove the `standby` section from the postgres cluster manifest.
### Turn a normal cluster into a standby
There is no way to transform a non-standby cluster to a standby cluster through
the operator. Adding the `standby` section to the manifest of a running
Postgres cluster will have no effect. But, as explained in the previous
paragraph it can be done manually through `patronictl edit-config`. This time,
by adding the `standby_cluster` section to the Patroni configuration. However,
the transformed standby cluster will not be doing any streaming. It will be in
standby mode and allow read-only transactions only.
## Sidecar Support ## Sidecar Support

10
pkg/cluster/k8sres.go
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@ -1048,11 +1048,13 @@ func (c *Cluster) getNumberOfInstances(spec *acidv1.PostgresSpec) int32 {
cur := spec.NumberOfInstances cur := spec.NumberOfInstances
newcur := cur newcur := cur
/* Limit the max number of pods to one, if this is standby-cluster */
if spec.StandbyCluster != nil { if spec.StandbyCluster != nil {
c.logger.Info("Standby cluster can have maximum of 1 pod") if newcur > 1 {
min = 1 c.logger.Warningf("operator only supports standby clusters with 1 pod")
max = 1 } else {
min = newcur
max = newcur
}
} }
if max >= 0 && newcur > max { if max >= 0 && newcur > max {
newcur = max newcur = max