8.5. Pgpool-II on Kubernetes

8.5.4.1. Configure Pgpool-II using environment variables

Kubernetes environment variables can be passed to a container in a pod. You can define environment variables in the deployment manifest to configure Pgpool-II's parameters. pgpool_deploy.yaml is an example of a Deployment manifest. You can download pgpool_deploy.yaml and specify environment variables in this manifest file.

$ curl -LO https://raw.githubusercontent.com/pgpool/pgpool2_on_k8s/master/pgpool_deploy.yaml
   

Environment variables starting with PGPOOL_PARAMS_ can be converted to Pgpool-II's configuration parameters and these values can override the default configurations.

• The Pgpool-II container Docker images is build with streaming replication mode. By default, load balancing, connection pooling and streaming replication check is enabled.

• Specify only two backend nodes. Specify the Primary Service name to backend_hostname0. Specify the Replica Service name to backend_hostname1. Because failover is managed by Kubernetes, specify DISALLOW_TO_FAILOVER flag to backend_flag for both of the two nodes and ALWAYS_PRIMARY flag to backend_flag0. Configure appropriate backend_weight as usual. You don't need to specify backend_data_directory.

  For example, the following environment variables defined in manifest,

  env:
  - name: PGPOOL_PARAMS_BACKEND_HOSTNAME0
    value: "hippo"
  - name: PGPOOL_PARAMS_BACKEND_HOSTNAME1
    value: "hippo-replica"
  - name: PGPOOL_PARAMS_BACKEND_FLAG0
    value: "ALWAYS_PRIMARY|DISALLOW_TO_FAILOVER"
  - name: PGPOOL_PARAMS_BACKEND_FLAG1
    value: "DISALLOW_TO_FAILOVER"
       

  will be convert to the following configuration parameters in pgpool.conf.

  backend_hostname0='hippo'
  backend_hostname1='hippo-replica'
  backend_flag0='ALWAYS_PRIMARY|DISALLOW_TO_FAILOVER'
  backend_flag1='DISALLOW_TO_FAILOVER'
       

• Specify a PostgreSQL user name and password to perform streaming replication check. For the security reasons, we recommend that you specify a encrypted password.

  - name: PGPOOL_PARAMS_SR_CHECK_USER
    value: "PostgreSQL user name"
  - name: PGPOOL_PARAMS_SR_CHECK_PASSWORD
    value: "encrypted PostgreSQL user's password"
       

  Alternatively, you can create a secret and use this secret as environment variables.

• Since health check is performed by Kubernetes, Pgpool-II's health check should be disabled. Because the default value is off, we don't need to set this parameter.

• By default, the following environment variables will be set when Pgpool-II container is started.

  export PGPOOL_PARAMS_LISTEN_ADDRESSES=*
  export PGPOOL_PARAMS_SR_CHECK_USER=${POSTGRES_USER:-"postgres"}
  export PGPOOL_PARAMS_SOCKET_DIR=/var/run/postgresql
  export PGPOOL_PARAMS_PCP_SOCKET_DIR=/var/run/postgresql
       

8.5.4.2. Configure Pgpool-II using ConfigMap

Alternatively, you can use a Kubernetes ConfigMap to store entire configuration files, i.e. pgpool.conf, pcp.conf, pool_passwd and pool_hba.conf. The ConfigMap can be mounted to Pgpool-II's container as a volume.

You can download the example manifest files that define the ConfigMap and Deployment from repository.

curl -LO https://raw.githubusercontent.com/pgpool/pgpool2_on_k8s/master/pgpool_configmap.yaml
curl -LO https://raw.githubusercontent.com/pgpool/pgpool2_on_k8s/master/pgpool_deploy_with_mount_configmap.yaml
   

The manifest that defines the ConfigMap is in the following format. You can update it based on your configuration preferences.

apiVersion: v1
kind: ConfigMap
metadata:
  name: pgpool-config
  labels:
    app: pgpool-config
data:
  pgpool.conf: |-
    listen_addresses = '*'
    port = 9999
    socket_dir = '/var/run/postgresql'
    pcp_listen_addresses = '*'
    pcp_port = 9898
    pcp_socket_dir = '/var/run/postgresql'
    backend_hostname0 = 'hippo'
    backend_port0 = 5432
    backend_weight0 = 1
    backend_flag0 = 'ALWAYS_PRIMARY|DISALLOW_TO_FAILOVER'
    backend_hostname1 = 'hippo-replica'
    backend_port1 = 5432
    backend_weight1 = 1
    backend_flag1 = 'DISALLOW_TO_FAILOVER'
    sr_check_user = 'postgres'
    sr_check_period = 10
    enable_pool_hba = on
    master_slave_mode = on
    num_init_children = 32
    max_pool = 4
    child_life_time = 300
    child_max_connections = 0
    connection_life_time = 0
    client_idle_limit = 0
    connection_cache = on
    load_balance_mode = on
  pcp.conf: |-
    postgres:e8a48653851e28c69d0506508fb27fc5
  pool_passwd: |-
    postgres:md53175bce1d3201d16594cebf9d7eb3f9d
  pool_hba.conf: |-
    local   all         all                               trust
    host    all         all         127.0.0.1/32          trust
    host    all         all         ::1/128               trust
    host    all         all         0.0.0.0/0             md5
   

First, you need to create the ConfigMap before referencing it to Pgpool-II pod.

kubectl apply -f pgpool_configmap.yaml
   

Once you have created the ConfigMap, you can deploy Pgpool-II pod and mount the ConfigMap to Pgpool-II pod as a volume.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: pgpool
  ...
        volumeMounts:
        - name: pgpool-config
          mountPath: /usr/local/pgpool-II/etc
      ...
      volumes:
      - name: pgpool-config
        configMap:
          name: pgpool-config
   

pgpool_deploy_with_mount_configmap.yaml is an example of a Deployment manifest that mounts the created ConfigMap to the Pgpool-II pod.

kubectl apply -f pgpool_deploy_with_mount_configmap.yaml
   

After deploying Pgpool-II, you can see the Pgpool-II pod and services using kubectl get pod and kubectl get svc command.