Distributed Logs

By default, Postgres logs would be written to the ephemeral storage of the Patroni container, and could be accessed in the usual manner. However, in a modern environment this is not ideal because of the ephemeral nature of the storage, and because logs from all pods are on different locations.

StackGres has created a technology stack to send Postgres and Patroni logs to a separate location, called a Distributed Logs Server. This server is represented by the SGDistributedLogs CRD. A distributed log server is a separate Postgres instance, optimized for log storage, using the time-series Timescale extension to support high volume injection and automatic partitioning of logs, as well as log rotation.

This is all handled transparently for you, just go ahead and create the file sgdistributedlogs-server1.yaml to use this functionality:

apiVersion: stackgres.io/v1
kind: SGDistributedLogs
  namespace: demo
  name: distributedlogs
    size: 50Gi

and deploy it to Kubernetes:

kubectl apply -f sgdistributedlogs-server1.yaml

This command will create multiple Kubernetes resources. In particular, it will create a pod for storing the mentioned distributed logs:

kubectl -n demo get pods
NAME                READY   STATUS    RESTARTS   AGE
distributedlogs-0   3/3     Running   1          73s

Distributed logs server are multi-tenant: you may reference a distributed log server from more than one cluster. If a distributed log server is used, Postgres logs will not be stored in the ephemeral pod storage (except temporarily in small buffers).

To see the distributed logs, you may view them in the web console, or connect via psql and query them with SQL.

Accessing Postgres and Patroni Logs

In the admin UI, accessing the logs is easy: go to the web console, navigate to the cluster, and click on the Logs pane.

But now, let’s do it from the CLI. You are able to connect to the distributed logs database and query the logs with SQL. Indeed, the SGDistributedLogs resource that we created before led to the creation of a specialized SGCluster, used for logs. You connect to this cluster through its read and write service, similar to any other StackGres cluster. For the distributed logs, the host name equals the name specified in the SGDistributedLogs resource, in our case distributedlogs.

In the same way as before, we can retrieve the connection password from the distributedlogs secret:

$ PGPASSWORD=$(kubectl -n demo get secret distributedlogs --template '{{ printf "%s" (index .data "superuser-password" | base64decode) }}')

Then, we can connect to our distributed logs cluster via psql:

$ kubectl -n demo run psql --env $PGPASSWORD --rm -it --image ongres/postgres-util --restart=Never -- psql -h distributedlogs postgres postgres

Now that we’re in psql, we can query the logs with SQL. The following commands will list the databases, connect to the database for our current cluster, count the Postgres log entries, describe the logs table, and select all logs of type ERROR. There will be one database per every cluster that is sending logs to this distributed logs server, with the naming scheme <namespace>_<cluster>. You can generate ERROR logs by typing any SQL error into the SQL console of the source cluster (not this one). Logs may take a few seconds to propagate.

\c demo_cluster
\dt log_postgres
select count(*) from log_postgres;
select * from log_postgres where error_severity = 'ERROR';

\l+ Lists the databases (with additional details)
\c <db> Connects to a database
\dt <table> Lists all tables (if <table> isn’t specified) or a specific table