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Continuous Archiving with wal-g

KubeDB PostgreSQL also supports continuous archiving using wal-g . Now wal-g supports only amazon S3 as cloud storage.

Before You Begin

At first, you need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using minikube.

Now, install KubeDB cli on your workstation and KubeDB operator in your cluster following the steps here.

To keep things isolated, this tutorial uses a separate namespace called demo throughout this tutorial.

$ kubectl create ns demo
namespace "demo" created

$ kubectl get ns demo
NAME    STATUS  AGE
demo    Active  5s

Note: Yaml files used in this tutorial are stored in docs/examples/postgres folder in GitHub repository kubedb/cli.

Create PostgreSQL with Continuous Archiving

Below is the Postgres object created with Continuous Archiving support.

apiVersion: kubedb.com/v1alpha1
kind: Postgres
metadata:
  name: wal-postgres
  namespace: demo
spec:
  version: "9.6-v1"
  replicas: 2
  storage:
    storageClassName: "standard"
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 50Mi
  archiver:
    storage:
      storageSecretName: s3-secret
      s3:
        bucket: kubedb

Here,

• spec.archiver.storage specifies storage information that will be used by wal-g
  • storage.storageSecretName points to the Secret containing the credentials for cloud storage destination.
  • storage.s3.bucket points to the bucket name used to store continuous archiving data.

What is this Continuous Archiving

PostgreSQL maintains a write ahead log (WAL) in the pg_xlog/ subdirectory of the cluster’s data directory. The existence of the log makes it possible to use a third strategy for backing up databases and if recovery is needed, restore from the backed-up WAL files to bring the system to a current state.

Continuous Archiving Setup

KubeDB PostgreSQL supports wal-g for this continuous archiving.

Following additional parameters are set in postgresql.conf for primary server

archive_command = 'wal-g wal-push %p'
archive_timeout = 60

And following additional is set in recovery.conf for standby server

restore_command = 'wal-g wal-fetch %f %p'

Here, these commands are used to push and pull WAL files respectively from cloud.

wal-g is used to handle this continuous archiving mechanism. For this we need storage Secret and need to provide storage backend information.

Archiver Storage Secret

Storage Secret should contain credentials that will be used to access storage destination.

Storage Secret for wal-g is needed with following 2 keys:

$ echo -n '<your-aws-access-key-id-here>' > AWS_ACCESS_KEY_ID
$ echo -n '<your-aws-secret-access-key-here>' > AWS_SECRET_ACCESS_KEY
$ kubectl create secret -n demo generic s3-secret \
    --from-file=./AWS_ACCESS_KEY_ID \
    --from-file=./AWS_SECRET_ACCESS_KEY
secret "s3-secret" created

$ kubectl get secret -n demo s3-secret -o yaml
apiVersion: v1
data:
  AWS_ACCESS_KEY_ID: PHlvdXItYXdzLWFjY2Vzcy1rZXktaWQtaGVyZT4=
  AWS_SECRET_ACCESS_KEY: PHlvdXItYXdzLXNlY3JldC1hY2Nlc3Mta2V5LWhlcmU+
kind: Secret
metadata:
  creationTimestamp: 2018-02-06T09:12:37Z
  name: s3-secret
  namespace: demo
  resourceVersion: "59225"
  selfLink: /api/v1/namespaces/demo/secrets/s3-secret
  uid: dfbe6b06-0b1d-11e8-9fb9-42010a800064
type: Opaque

Archiver Storage Backend

wal-g supports only S3 cloud providers.

To configure this backend, following parameters are available:

Now create this Postgres object with Continuous Archiving support.

$ kubectl create -f https://raw.githubusercontent.com/kubedb/cli/0.9.0/docs/examples/postgres/snapshot/wal-postgres.yaml
postgres "wal-postgres" created

When database is ready, wal-g takes a base backup and uploads it to cloud storage defined by storage backend.

Archived data is stored in a folder called {bucket}/{prefix}/kubedb/{namespace}/{postgres-name}/archive/.

you can see continuous archiving data stored in S3 bucket.

From the above image, you can see that the archived data is stored in a folder kubedb/kubedb/demo/wal-postgres/archive.

Cleaning up

To cleanup the Kubernetes resources created by this tutorial, run:

$ kubectl patch -n demo pg/wal-postgres -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
$ kubectl delete -n demo pg/wal-postgres

$ kubectl delete -n demo secret/s3-secret
$ kubectl delete ns demo

Next Steps

• Learn about initializing PostgreSQL from WAL files stored in cloud.