Testing PostgreSQL read replication

This provides a Docker Compose file that starts up a PostgreSQL primary server and a single read replica.

We can use this to test how the HGE Server and Console behave when communicating with a read replica.

Starting and stopping

To start them, run the following from this directory:

docker compose up --wait

To stop them, run:

docker compose down

(Add -v to delete the data too.)

Connecting

Ports

To connect to the databases, you will need to get the ports.

The primary port can be found by running:

docker compose port postgres-primary 5432

The replica port can be found by running:

docker compose port postgres-replica 5432

Note that these ports may change if you restart the server.

Credentials

The database username is postgres, and the password is password, for both the primary and the replica.

Experimenting with the Hasura GraphQL Engine

Run HGE as follows:

cabal run graphql-engine:exe:graphql-engine -- \
  --metadata-database-url="postgresql://postgres:password@$(docker compose --project-directory=server/test-manual/postgres-replicas port postgres-primary 5432)" \
  serve \
  --enable-console \
  --console-assets-dir=$PWD/frontend/dist/apps/server-assets-console

Then run the following to get the replica database connection URL, and add it as the "default" data source.

echo "postgresql://postgres:password@$(docker compose --project-directory=server/test-manual/postgres-replicas port postgres-primary 5432)"