antonchernik/postgres repository overview

⁠Postgres

⁠What is PostgreSQL?

PostgreSQL, often simply "Postgres", is an object-relational database management system (ORDBMS) with an emphasis on extensibility and standards-compliance. As a database server, its primary function is to store data, securely and supporting best practices, and retrieve it later, as requested by other software applications, be it those on the same computer or those running on another computer across a network (including the Internet). It can handle workloads ranging from small single-machine applications to large Internet-facing applications with many concurrent users. Recent versions also provide replication of the database itself for security and scalability.

PostgreSQL implements the majority of the SQL:2011 standard, is ACID-compliant and transactional (including most DDL statements) avoiding locking issues using multiversion concurrency control (MVCC), provides immunity to dirty reads and full serializability; handles complex SQL queries using many indexing methods that are not available in other databases; has updateable views and materialized views, triggers, foreign keys; supports functions and stored procedures, and other expandability, and has a large number of extensions written by third parties. In addition to the possibility of working with the major proprietary and open source databases, PostgreSQL supports migration from them, by its extensive standard SQL support and available migration tools. And if proprietary extensions had been used, by its extensibility that can emulate many through some built-in and third-party open source compatibility extensions, such as for Oracle.

⁠How to use this image

⁠start a postgres instance

$ docker run --name some-postgres -e POSTGRES_PASSWORD=mysecretpassword -d antonchernik/postgres

The default postgres user and database are created in the entrypoint with initdb.

⁠... or via psql

$ docker run -it --rm --network some-network antonchernik/postgres psql -h some-postgres -U antonchernik/postgres
psql (12.2-2)
Type "help" for help.

postgres=# SELECT 1;
 ?column? 
----------
        1
(1 row)

⁠... via docker stack deploy⁠ or docker-compose⁠

Example stack.yml for antonchernik/postgres:

# Use postgres/example user/password credentials
version: '3.1'

services:

  db:
    image: antonchernik/postgres
    restart: always
    environment:
      POSTGRES_PASSWORD: example

  adminer:
    image: adminer
    restart: always
    ports:
      - 8080:8080

⁠How to extend this image

There are many ways to extend the antonchernik/postgres image. Without trying to support every possible use case, here are just a few that we have found useful.

⁠Environment Variables

The PostgreSQL image uses several environment variables which are easy to miss. While none of the variables are required, they may significantly aid you in using the image.

Warning: the Docker specific variables will only have an effect if you start the container with a data directory that is empty; any pre-existing database will be left untouched on container startup.

⁠POSTGRES_PASSWORD

This environment variable is required for you to use the PostgreSQL image. It must not be empty or undefined. This environment variable sets the superuser password for PostgreSQL. The default superuser is defined by the POSTGRES_USER environment variable.

Note 1: The PostgreSQL image sets up trust authentication locally so you may notice a password is not required when connecting from localhost (inside the same container). However, a password will be required if connecting from a different host/container.

Note 2: This variable defines the superuser password in the PostgreSQL instance, as set by the initdb script during initial container startup. It has no effect on the PGPASSWORD environment variable that may be used by the psql client at runtime, as described at https://www.postgresql.org/docs/10/static/libpq-envars.html⁠. PGPASSWORD, if used, will be specified as a separate environment variable.

⁠POSTGRES_USER

This optional environment variable is used in conjunction with POSTGRES_PASSWORD to set a user and its password. This variable will create the specified user with superuser power and a database with the same name. If it is not specified, then the default user of postgres will be used.

Be aware that if this parameter is specified, PostgreSQL will still show The files belonging to this database system will be owned by user "postgres" during initialization. This refers to the Linux system user (from /etc/passwd in the image) that the postgres daemon runs as, and as such is unrelated to the POSTGRES_USER option. See the section titled "Arbitrary --user Notes" for more details.

⁠POSTGRES_DB

This optional environment variable can be used to define a different name for the default database that is created when the image is first started. If it is not specified, then the value of POSTGRES_USER will be used.

⁠POSTGRES_INITDB_ARGS

This optional environment variable can be used to send arguments to postgres initdb. The value is a space separated string of arguments as postgres initdb would expect them. This is useful for adding functionality like data page checksums: -e POSTGRES_INITDB_ARGS="--data-checksums".

⁠POSTGRES_INITDB_WALDIR

This optional environment variable can be used to define another location for the Postgres transaction log. By default the transaction log is stored in a subdirectory of the main Postgres data folder (PGDATA). Sometimes it can be desireable to store the transaction log in a different directory which may be backed by storage with different performance or reliability characteristics.

Note: on PostgreSQL 9.x, this variable is POSTGRES_INITDB_XLOGDIR (reflecting the changed name of the --xlogdir flag to --waldir in PostgreSQL 10+⁠).

⁠POSTGRES_HOST_AUTH_METHOD

This optional variable can be used to control the auth-method for host connections for all databases, all users, and all addresses. If unspecified then md5 password authentication⁠ is used. On an uninitialized database, this will populate pg_hba.conf via this approximate line:

echo "host all all all $POSTGRES_HOST_AUTH_METHOD" >> pg_hba.conf

See the PostgreSQL documentation on pg_hba.conf⁠ for more information about possible values and their meanings.

Note 1: It is not recommended to use trust⁠ since it allows anyone to connect without a password, even if one is set (like via POSTGRES_PASSWORD). For more information see the PostgreSQL documentation on Trust Authentication⁠.

Note 2: If you set POSTGRES_HOST_AUTH_METHOD to trust, then POSTGRES_PASSWORD is not required.

⁠PGDATA

This optional variable can be used to define another location - like a subdirectory - for the database files. The default is /var/lib/postgresql/data. If the data volume you're using is a filesystem mountpoint (like with GCE persistent disks) or remote folder that cannot be chowned to the postgres user (like some NFS mounts), Postgres initdb recommends a subdirectory be created to contain the data.

For example:

$ docker run -d \
	--name some-postgres \
	-e POSTGRES_PASSWORD=mysecretpassword \
	-e PGDATA=/var/lib/postgresql/data/pgdata \
	-v /custom/mount:/var/lib/postgresql/data \
	antonchernik/postgres

This is an environment variable that is not Docker specific. Because the variable is used by the antonchernik/postgres server binary (see the PostgreSQL docs⁠), the entrypoint script takes it into account.

⁠Docker Secrets

As an alternative to passing sensitive information via environment variables, _FILE may be appended to some of the previously listed environment variables, causing the initialization script to load the values for those variables from files present in the container. In particular, this can be used to load passwords from Docker secrets stored in /run/secrets/<secret_name> files. For example:

$ docker run --name some-postgres -e POSTGRES_PASSWORD_FILE=/run/secrets/postgres-passwd -d antonchernik/postgres

Currently, this is only supported for POSTGRES_INITDB_ARGS, POSTGRES_PASSWORD, POSTGRES_USER, and POSTGRES_DB.

⁠Initialization scripts

If you would like to do additional initialization in an image derived from this one, add one or more *.sql, *.sql.gz, or *.sh scripts under /docker-entrypoint-initdb.d (creating the directory if necessary). After the entrypoint calls initdb to create the default postgres user and database, it will run any *.sql files, run any executable *.sh scripts, and source any non-executable *.sh scripts found in that directory to do further initialization before starting the service.

Warning: scripts in /docker-entrypoint-initdb.d are only run if you start the container with a data directory that is empty; any pre-existing database will be left untouched on container startup. One common problem is that if one of your /docker-entrypoint-initdb.d scripts fails (which will cause the entrypoint script to exit) and your orchestrator restarts the container with the already initialized data directory, it will not continue on with your scripts.

For example, to add an additional user and database, add the following to /docker-entrypoint-initdb.d/init-user-db.sh:

#!/bin/bash
set -e

psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" <<-EOSQL
	CREATE USER docker;
	CREATE DATABASE docker;
	GRANT ALL PRIVILEGES ON DATABASE docker TO docker;
EOSQL

These initialization files will be executed in sorted name order as defined by the current locale, which defaults to en_US.utf8. Any *.sql files will be executed by POSTGRES_USER, which defaults to the postgres superuser. It is recommended that any psql commands that are run inside of a *.sh script be executed as POSTGRES_USER by using the --username "$POSTGRES_USER" flag. This user will be able to connect without a password due to the presence of trust authentication for Unix socket connections made inside the container.

Additionally, as of docker-library/postgres#253⁠, these initialization scripts are run as the postgres user (or as the "semi-arbitrary user" specified with the --user flag to docker run; see the section titled "Arbitrary --user Notes" for more details). Also, as of docker-library/postgres#440⁠, the temporary daemon started for these initialization scripts listens only on the Unix socket, so any psql usage should drop the hostname portion (see docker-library/postgres#474 (comment)⁠ for example).

⁠Supported tags and respective Dockerfile links

* 12.2-2-ubuntu-amd64 Dockerfile (library/postgres/12/ubuntu-amd64/Dockerfile)⁠
Trivy security report (library/postgres/12/ubuntu-amd64/trivy.txt)⁠