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README.md

README.md

PostgreSQL Docker image

This repository contains Dockerfiles for PostgreSQL images for general usage and OpenShift. Users can choose between RHEL and CentOS based images.

Environment variables and volumes

The image recognizes the following environment variables that you can set during initialization by passing -e VAR=VALUE to the Docker run command.

Variable name Description
POSTGRESQL_USER User name for PostgreSQL account to be created
POSTGRESQL_PASSWORD Password for the user account
POSTGRESQL_DATABASE Database name
POSTGRESQL_ADMIN_PASSWORD Password for the postgres admin account (optional)

The following environment variables influence the PostgreSQL configuration file. They are all optional.

Variable name Description Default
POSTGRESQL_MAX_CONNECTIONS The maximum number of client connections allowed. This also sets the maximum number of prepared transactions. 100
POSTGRESQL_SHARED_BUFFERS Sets how much memory is dedicated to PostgreSQL to use for caching data 32M
POSTGRESQL_EFFECTIVE_CACHE_SIZE Set to an estimate of how much memory is available for disk caching by the operating system and within the database itself 128M

You can also set the following mount points by passing the -v /host:/container flag to Docker.

Volume mount point Description
/var/lib/pgsql/data PostgreSQL database cluster directory

Notice: When mouting a directory from the host into the container, ensure that the mounted directory has the appropriate permissions and that the owner and group of the directory matches the user UID or name which is running inside the container.

Usage

For this, we will assume that you are using the centos/postgresql-94-centos7 image. If you want to set only the mandatory environment variables and not store the database in a host directory, execute the following command:

$ docker run -d --name postgresql_database -e POSTGRESQL_USER=user -e POSTGRESQL_PASSWORD=pass -e POSTGRESQL_DATABASE=db -p 5432:5432 centos/postgresql-94-centos7

This will create a container named postgresql_database running PostgreSQL with database db and user with credentials user:pass. Port 5432 will be exposed and mapped to the host. If you want your database to be persistent across container executions, also add a -v /host/db/path:/var/lib/pgsql/data argument. This will be the PostgreSQL database cluster directory.

If the database cluster directory is not initialized, the entrypoint script will first run initdb and setup necessary database users and passwords. After the database is initialized, or if it was already present, postgres is executed and will run as PID 1. You can stop the detached container by running docker stop postgresql_database.

PostgreSQL auto-tuning

When the PostgreSQL image is run with the --memory parameter set and if there are no values provided for POSTGRESQL_SHARED_BUFFERS and POSTGRESQL_EFFECTIVE_CACHE_SIZE those values are automatically calculated based on the value provided in the --memory parameter.

The values are calculated based on the upstream formulas. For the shared_buffers we use 1/4 of given memory and for the effective_cache_size we set the value to 1/2 of the given memory.

PostgreSQL admin account

The admin account postgres has no password set by default, only allowing local connections. You can set it by setting the POSTGRESQL_ADMIN_PASSWORD environment variable when initializing your container. This will allow you to login to the postgres account remotely. Local connections will still not require a password.

Changing passwords

Since passwords are part of the image configuration, the only supported method to change passwords for the database user (POSTGRESQL_USER) and postgres admin user is by changing the environment variables POSTGRESQL_PASSWORD and POSTGRESQL_ADMIN_PASSWORD, respectively.

Changing database passwords through SQL statements or any way other than through the environment variables aforementioned will cause a mismatch between the values stored in the variables and the actual passwords. Whenever a database container starts it will reset the passwords to the values stored in the environment variables.

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