postgres-operator/docs/user.md

User Guide

Learn how to work with the Postgres Operator in a Kubernetes (K8s) environment.

Create a manifest for a new PostgreSQL cluster

Make sure you have set up the operator. Then you can create a new Postgres cluster by applying manifest like this minimal example:

apiVersion: "acid.zalan.do/v1"
kind: postgresql
metadata:
  name: acid-minimal-cluster
spec:
  teamId: "acid"
  volume:
    size: 1Gi
  numberOfInstances: 2
  users:
    # database owner
    zalando:
    - superuser
    - createdb

    # role for application foo
    foo_user: # or 'foo_user: []'

  #databases: name->owner
  databases:
    foo: zalando
  postgresql:
    version: "12"

Once you cloned the Postgres Operator repository you can find this example also in the manifests folder:

kubectl create -f manifests/minimal-postgres-manifest.yaml

Make sure, the spec section of the manifest contains at least a teamId, the numberOfInstances and the postgresql object with the version specified. The minimum volume size to run the postgresql resource on Elastic Block Storage (EBS) is 1Gi.

Note, that the name of the cluster must start with the teamId and -. At Zalando we use team IDs (nicknames) to lower the chance of duplicate cluster names and colliding entities. The team ID would also be used to query an API to get all members of a team and create database roles for them.

Watch pods being created

kubectl get pods -w --show-labels

Connect to PostgreSQL

With a port-forward on one of the database pods (e.g. the master) you can connect to the PostgreSQL database. Use labels to filter for the master pod of our test cluster.

# get name of master pod of acid-minimal-cluster
export PGMASTER=$(kubectl get pods -o jsonpath={.items..metadata.name} -l application=spilo,cluster-name=acid-minimal-cluster,spilo-role=master)

# set up port forward
kubectl port-forward $PGMASTER 6432:5432

Open another CLI and connect to the database. Use the generated secret of the postgres robot user to connect to our acid-minimal-cluster master running in Minikube. As non-encrypted connections are rejected by default set the SSL mode to require:

export PGPASSWORD=$(kubectl get secret postgres.acid-minimal-cluster.credentials -o 'jsonpath={.data.password}' | base64 -d)
export PGSSLMODE=require
psql -U postgres -p 6432

Defining database roles in the operator

Postgres Operator allows defining roles to be created in the resulting database cluster. It covers three use-cases:

• manifest roles: create application roles specific to the cluster described in the manifest.
• infrastructure roles: create application roles that should be automatically created on every cluster managed by the operator.
• teams API roles: automatically create users for every member of the team owning the database cluster.

In the next sections, we will cover those use cases in more details.

Manifest roles

Manifest roles are defined directly in the cluster manifest. See minimal postgres manifest for an example of zalando role, defined with superuser and createdb flags.

Manifest roles are defined as a dictionary, with a role name as a key and a list of role options as a value. For a role without any options it is best to supply the empty list []. It is also possible to leave this field empty as in our example manifests. In certain cases such empty field may be missing later removed by K8s due to the null value it gets (foobar_user: is equivalent to foobar_user: null).

The operator accepts the following options: superuser, inherit, login, nologin, createrole, createdb, replication, bypassrls.

By default, manifest roles are login roles (aka users), unless nologin is specified explicitly.

The operator automatically generates a password for each manifest role and places it in the secret named {username}.{team}-{clustername}.credentials.postgresql.acid.zalan.do in the same namespace as the cluster. This way, the application running in the K8s cluster and connecting to Postgres can obtain the password right from the secret, without ever sharing it outside of the cluster.

At the moment it is not possible to define membership of the manifest role in other roles.

Infrastructure roles

An infrastructure role is a role that should be present on every PostgreSQL cluster managed by the operator. An example of such a role is a monitoring user. There are two ways to define them:

• With the infrastructure roles secret only
• With both the the secret and the infrastructure role ConfigMap.

Infrastructure roles secret

The infrastructure roles secret is specified by the infrastructure_roles_secret_name parameter. The role definition looks like this (values are base64 encoded):

user1: ZGJ1c2Vy
password1: c2VjcmV0
inrole1: b3BlcmF0b3I=

The block above describes the infrastructure role 'dbuser' with password 'secret' that is a member of the 'operator' role. For the following definitions one must increase the index, i.e. the next role will be defined as 'user2' and so on. The resulting role will automatically be a login role.

Note that with definitions that solely use the infrastructure roles secret there is no way to specify role options (like superuser or nologin) or role memberships. This is where the ConfigMap comes into play.

Secret plus ConfigMap

A ConfigMap allows for defining more details regarding the infrastructure roles. Therefore, one should use the new style that specifies infrastructure roles using both the secret and a ConfigMap. The ConfigMap must have the same name as the secret. The secret should contain an entry with 'rolename:rolepassword' for each role.

dbuser: c2VjcmV0

And the role description for that user should be specified in the ConfigMap.

data:
  dbuser: |
    inrole: [operator, admin]  # following roles will be assigned to the new user
    user_flags:
    - createdb
    db_parameters:  # db parameters, applied for this particular user
      log_statement: all    

One can allow membership in multiple roles via the inrole array parameter, define role flags via the user_flags list and supply per-role options through the db_parameters dictionary. All those parameters are optional.

Both definitions can be mixed in the infrastructure role secret, as long as your new-style definition can be clearly distinguished from the old-style one (for instance, do not name new-style roles userN).

Since an infrastructure role is created uniformly on all clusters managed by the operator, it makes no sense to define it without the password. Such definitions will be ignored with a prior warning.

See infrastructure roles secret and infrastructure roles configmap for the examples.

Teams API roles

These roles are meant for database activity of human users. It's possible to configure the operator to automatically create database roles for lets say all employees of one team. They are not listed in the manifest and there are no K8s secrets created for them. Instead they would use an OAuth2 token to connect. To get all members of the team the operator queries a defined API endpoint that returns usernames. A minimal Teams API should work like this:

/.../<teamname> -> ["name","anothername"]

A "fake" Teams API deployment is provided in the manifests folder to set up a basic API around whatever services is used for user management. The Teams API's URL is set in the operator's configuration and enable_teams_api must be set to true. There are more settings available to choose superusers, group roles, PAM configuration etc. An OAuth2 token can be passed to the Teams API via a secret. The name for this secret is configurable with the oauth_token_secret_name parameter.

Resource definition

The compute resources to be used for the Postgres containers in the pods can be specified in the postgresql cluster manifest.

spec:
  resources:
    requests:
      cpu: 10m
      memory: 100Mi
    limits:
      cpu: 300m
      memory: 300Mi

The minimum limits to properly run the postgresql resource are configured to 250m for cpu and 250Mi for memory. If a lower value is set in the manifest the operator will raise the limits to the configured minimum values. If no resources are defined in the manifest they will be obtained from the configured default requests.

Use taints and tolerations for dedicated PostgreSQL nodes

To ensure Postgres pods are running on nodes without any other application pods, you can use taints and tolerations and configure the required toleration in the manifest.

spec:
  tolerations:
  - key: postgres
    operator: Exists
    effect: NoSchedule

How to clone an existing PostgreSQL cluster

You can spin up a new cluster as a clone of the existing one, using a clone section in the spec. There are two options here:

• Clone from an S3 bucket (recommended)
• Clone directly from a source cluster

Note, that cloning can also be used for major version upgrades of PostgreSQL.

Clone from S3

Cloning from S3 has the advantage that there is no impact on your production database. A new Postgres cluster is created by restoring the data of another source cluster. If you create it in the same Kubernetes environment, use a different name.

spec:
  clone:
    uid: "efd12e58-5786-11e8-b5a7-06148230260c"
    cluster: "acid-batman"
    timestamp: "2017-12-19T12:40:33+01:00"

Here cluster is a name of a source cluster that is going to be cloned. A new cluster will be cloned from S3, using the latest backup before the timestamp. Note, that a time zone is required for timestamp in the format of +00:00 which is UTC. The uid field is also mandatory. The operator will use it to find a correct key inside an S3 bucket. You can find this field in the metadata of the source cluster:

apiVersion: acid.zalan.do/v1
kind: postgresql
metadata:
  name: acid-test-cluster
  uid: efd12e58-5786-11e8-b5a7-06148230260c

For non AWS S3 following settings can be set to support cloning from other S3 implementations:

spec:
  clone:
    uid: "efd12e58-5786-11e8-b5a7-06148230260c"
    cluster: "acid-batman"
    timestamp: "2017-12-19T12:40:33+01:00"
    s3_endpoint: https://s3.acme.org
    s3_access_key_id: 0123456789abcdef0123456789abcdef
    s3_secret_access_key: 0123456789abcdef0123456789abcdef
    s3_force_path_style: true

Clone directly

Another way to get a fresh copy of your source DB cluster is via basebackup. To use this feature simply leave out the timestamp field from the clone section. The operator will connect to the service of the source cluster by name. If the cluster is called test, then the connection string will look like host=test port=5432), which means that you can clone only from clusters within the same namespace.

spec:
  clone:
    cluster: "acid-batman"

Be aware that on a busy source database this can result in an elevated load!

Setting up a standby cluster

Standby cluster is a Patroni feature that first clones a database, and keeps replicating changes afterwards. As the replication is happening by the means of archived WAL files (stored on S3 or the equivalent of other cloud providers), the standby cluster can exist in a different location than its source database. Unlike cloning, the PostgreSQL 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.

spec:
  standby:
    s3_wal_path: "s3 bucket path to the master"

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. 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.

Providing credentials of source cluster

A standby cluster is replicating the data (including users and passwords) from the source database and is read-only. The system and application users (like standby, postgres etc.) all have a password that does not match the credentials stored in secrets which are created by the operator. One solution is to create secrets beforehand and paste in the credentials of the source cluster. Otherwise, you will see errors in the Postgres logs saying users cannot log in and the operator logs will complain about not being able to sync resources.

When you only run a standby leader, you can safely ignore this, as it will be sorted out once the cluster is detached from the source. It is also harmless if you don’t plan it. But, when you created a standby replica, too, fix the credentials right away. WAL files will pile up on the standby leader if no connection can be established between standby replica(s). You can also edit the secrets after their creation. Find them by:

kubectl get secrets --all-namespaces | grep <standby-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.

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

Each cluster can specify arbitrary sidecars to run. These containers could be used for log aggregation, monitoring, backups or other tasks. A sidecar can be specified like this:

spec:
  sidecars:
    - name: "container-name"
      image: "company/image:tag"
      resources:
        limits:
          cpu: 500m
          memory: 500Mi
        requests:
          cpu: 100m
          memory: 100Mi
      env:
        - name: "ENV_VAR_NAME"
          value: "any-k8s-env-things"

In addition to any environment variables you specify, the following environment variables are always passed to sidecars:

• POD_NAME - field reference to metadata.name
• POD_NAMESPACE - field reference to metadata.namespace
• POSTGRES_USER - the superuser that can be used to connect to the database
• POSTGRES_PASSWORD - the password for the superuser

The PostgreSQL volume is shared with sidecars and is mounted at /home/postgres/pgdata.

Note: The operator will not create a cluster if sidecar containers are specified but globally disabled in the configuration. The enable_sidecars option must be set to true.

InitContainers Support

Each cluster can specify arbitrary init containers to run. These containers can be used to run custom actions before any normal and sidecar containers start. An init container can be specified like this:

spec:
  initContainers:
    - name: "container-name"
      image: "company/image:tag"
      env:
        - name: "ENV_VAR_NAME"
          value: "any-k8s-env-things"

initContainers accepts full v1.Container definition.

Note: The operator will not create a cluster if initContainers are specified but globally disabled in the configuration. The enable_init_containers option must be set to true.

Increase volume size

Postgres operator supports statefulset volume resize if you're using the operator on top of AWS. For that you need to change the size field of the volume description in the cluster manifest and apply the change:

spec:
  volume:
    size: 5Gi # new volume size

The operator compares the new value of the size field with the previous one and acts on differences.

You can only enlarge the volume with the process described above, shrinking is not supported and will emit a warning. After this update all the new volumes in the statefulset are allocated according to the new size. To enlarge persistent volumes attached to the running pods, the operator performs the following actions:

• call AWS API to change the volume size

• connect to pod using kubectl exec and resize filesystem with resize2fs.

Fist step has a limitation, AWS rate-limits this operation to no more than once every 6 hours. Note, that if the statefulset is scaled down before resizing the new size is only applied to the volumes attached to the running pods. The size of volumes that correspond to the previously running pods is not changed.

Logical backups

You can enable logical backups from the cluster manifest by adding the following parameter in the spec section:

spec:
  enableLogicalBackup: true

The operator will create and sync a K8s cron job to do periodic logical backups of this particular Postgres cluster. Due to the limitation of K8s cron jobs it is highly advisable to set up additional monitoring for this feature; such monitoring is outside the scope of operator responsibilities. See configuration reference and administrator documentation for details on how backups are executed.

Connection pool

The operator can create a database side connection pool for those applications, where an application side pool is not feasible, but a number of connections is high. To create a connection pool together with a database, modify the manifest:

spec:
  enableConnectionPool: true

This will tell the operator to create a connection pool with default configuration, through which one can access the master via a separate service {cluster-name}-pooler. In most of the cases provided default configuration should be good enough.

To configure a new connection pool, specify:

spec:
  connectionPool:
    # how many instances of connection pool to create
    number_of_instances: 2

    # in which mode to run, session or transaction
    mode: "transaction"

    # schema, which operator will create to install credentials lookup
    # function
    schema: "pooler"

    # user, which operator will create for connection pool
    user: "pooler"

    # resources for each instance
    resources:
      requests:
        cpu: 500m
        memory: 100Mi
      limits:
        cpu: "1"
        memory: 100Mi

By default pgbouncer is used to create a connection pool. To find out about pool modes see docs (but it should be general approach between different implementation).

Note, that using pgbouncer means meaningful resource CPU limit should be less than 1 core (there is a way to utilize more than one, but in K8S it's easier just to spin up more instances).

Custom TLS certificates

By default, the spilo image generates its own TLS certificate during startup. However, this certificate cannot be verified and thus doesn't protect from active MITM attacks. In this section we show how to specify a custom TLS certificate which is mounted in the database pods via a K8s Secret.

Before applying these changes, the operator must also be configured with the spilo_fsgroup set to the GID matching the postgres user group. If the value is not provided, the cluster will default to 103 which is the GID from the default spilo image.

Upload the cert as a kubernetes secret:

kubectl create secret tls pg-tls \
  --key pg-tls.key \
  --cert pg-tls.crt

Or with a CA:

kubectl create secret generic pg-tls \
  --from-file=tls.crt=server.crt \
  --from-file=tls.key=server.key \
  --from-file=ca.crt=ca.crt

Alternatively it is also possible to use cert-manager to generate these secrets.

Then configure the postgres resource with the TLS secret:

apiVersion: "acid.zalan.do/v1"
kind: postgresql

metadata:
  name: acid-test-cluster
spec:
  tls:
    secretName: "pg-tls"
    caFile: "ca.crt" # add this if the secret is configured with a CA

Certificate rotation is handled in the spilo image which checks every 5 minutes if the certificates have changed and reloads postgres accordingly.