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Short Description
A docker image for postgresql
Full Description

absolootly/docker-postgresql

Introduction

This docker image is derived from sameersbn and remodified to install on a flattened ubuntu 15.10 image on docker hub.

PostgreSQL is an object-relational database management system (ORDBMS) with an emphasis on extensibility and standards-compliance [source].

Getting started

Installation

Automated builds of the image are available on Dockerhub and is the recommended method of installation.

docker pull absolootly/docker-postgresql:latest

Alternatively you can build the image yourself.

docker build -t absolootly/postgresql:latest github.com/simontakite/docker-postgresql

Quickstart

Start PostgreSQL using:

docker run --name postgresql -itd --restart always \
  --publish 5432:5432 \
  --volume /srv/docker/postgresql:/var/lib/postgresql \
  absolootly/docker-postgresql:latest

Login to the PostgreSQL server using:

docker exec -it postgresql sudo -u postgres psql

Alternatively, you can use the sample docker-compose.yml file to start the container using Docker Compose

Persistence

For PostgreSQL to preserve its state across container shutdown and startup you should mount a volume at /var/lib/postgresql.

The Quickstart command already mounts a volume for persistence.

SELinux users should update the security context of the host mountpoint so that it plays nicely with Docker:

mkdir -p /srv/docker/postgresql
chcon -Rt svirt_sandbox_file_t /srv/docker/postgresql

Trusting local connections

By default connections to the PostgreSQL server need to authenticated using a password. If desired you can trust connections from the local network using the PG_TRUST_LOCALNET variable.

docker run --name postgresql -itd --restart always \
  --env 'PG_TRUST_LOCALNET=true' \
  absolootly/docker-postgresql:latest

Note

The local network here is network to which the container is attached. This has different meanings depending on the --net parameter specified while starting the container. In the default configuration, this parameter would trust connections from other containers on the docker0 bridge.

Setting postgres user password

By default the postgres user is not assigned a password and as a result you can only login to the PostgreSQL server locally. If you wish to login remotely to the PostgreSQL server as the postgres user, you will need to assign a password for the user using the PG_PASSWORD variable.

docker run --name postgresql -itd --restart always \
  --env 'PG_PASSWORD=passw0rd' \
  absolootly/docker-postgresql:latest

Note

  • When persistence is in use, PG_PASSWORD is effective on the first run.
  • This feature is only available in the latest and versions > 9.4-10

Creating database user

A new PostgreSQL database user can be created by specifying the DB_USER and DB_PASS variables while starting the container.

docker run --name postgresql -itd --restart always \
  --env 'DB_USER=dbuser' --env 'DB_PASS=dbuserpass' \
  absolootly/docker-postgresql:latest

Notes

  • The created user can login remotely
  • The container will error out if a password is not specified for the user
  • No changes will be made if the user already exists
  • Only a single user can be created at each launch

Creating databases

A new PostgreSQL database can be created by specifying the DB_NAME variable while starting the container.

docker run --name postgresql -itd --restart always \
  --env 'DB_NAME=dbname' \
  absolootly/docker-postgresql:latest

By default databases are created by copying the standard system database named template1. You can specify a different template for your database using the DB_TEMPLATE parameter. Refer to Template Databases for further information.

Additionally, more than one database can be created by specifying a comma separated list of database names in DB_NAME. For example, the following command creates two new databases named dbname1 and dbname2.

This feature is only available in releases greater than 9.1-1

docker run --name postgresql -itd --restart always \
  --env 'DB_NAME=dbname1,dbname2' \
  absolootly/docker-postgresql:latest

Granting user access to a database

If the DB_USER and DB_PASS variables are specified along with the DB_NAME variable, then the user specified in DB_USER will be granted access to all the databases listed in DB_NAME. Note that if the user and/or databases do not exist, they will be created.

docker run --name postgresql -itd --restart always \
  --env 'DB_USER=dbuser' --env 'DB_PASS=dbuserpass' \
  --env 'DB_NAME=dbname1,dbname2' \
  absolootly/docker-postgresql:latest

In the above example dbuser with be granted access to both the dbname1 and dbname2 databases.

Enabling extensions

The image also packages the postgres contrib module. A comma separated list of modules can be specified using the DB_EXTENSION parameter.

docker run --name postgresql -itd \
  --env 'DB_NAME=db1,db2' --env 'DB_EXTENSION=unaccent,pg_trgm' \
  absolootly/docker-postgresql:latest

The above command enables the unaccent and pg_trgm modules on the databases listed in DB_NAME, namely db1 and db2.

NOTE:

This option deprecates the DB_UNACCENT parameter.

Creating replication user

Similar to the creation of a database user, a new PostgreSQL replication user can be created by specifying the REPLICATION_USER and REPLICATION_PASS variables while starting the container.

docker run --name postgresql -itd --restart always \
  --env 'REPLICATION_USER=repluser' --env 'REPLICATION_PASS=repluserpass' \
  absolootly/docker-postgresql:latest

Notes

  • The created user can login remotely
  • The container will error out if a password is not specified for the user
  • No changes will be made if the user already exists
  • Only a single user can be created at each launch

It is a good idea to create a replication user even if you are not going to use it as it will allow you to setup slave nodes and/or generate snapshots and backups when the need arises.

Setting up a replication cluster

When the container is started, it is by default configured to act as a master node in a replication cluster. This means that you can scale your PostgreSQL database backend when the need arises without incurring any downtime. However do note that a replication user must exist on the master node for this to work.

Begin by creating the master node of our cluster:

docker run --name postgresql-master -itd --restart always \
  --env 'DB_USER=dbuser' --env 'DB_PASS=dbuserpass' --env 'DB_NAME=dbname' \
  --env 'REPLICATION_USER=repluser' --env 'REPLICATION_PASS=repluserpass' \
  absolootly/docker-postgresql:latest

Notice that no additional arguments are specified while starting the master node of the cluster.

To create a replication slave the REPLICATION_MODE variable should be set to slave and additionally the REPLICATION_HOST, REPLICATION_PORT, REPLICATION_SSLMODE, REPLICATION_USER and REPLICATION_PASS variables should be specified.

Create a slave node:

docker run --name postgresql-slave01 -itd --restart always \
  --link postgresql-master:master \
  --env 'REPLICATION_MODE=slave' --env 'REPLICATION_SSLMODE=prefer' \
  --env 'REPLICATION_HOST=master' --env 'REPLICATION_PORT=5432'  \
  --env 'REPLICATION_USER=repluser' --env 'REPLICATION_PASS=repluserpass' \
  absolootly/docker-postgresql:latest

In the above command, we used docker links so that we can address the master node using the master alias in REPLICATION_HOST.

Note

  • The default value of REPLICATION_PORT is 5432
  • The default value of REPLICATION_SSLMODE is prefer
  • The value of REPLICATION_USER and REPLICATION_PASS should be the same as the ones specified on the master node.
  • With persistence in use, if the container is stopped and started, for the container continue to function as a slave you need to ensure that REPLICATION_MODE=slave is defined in the containers environment. In the absense of which the slave configuration will be turned off and the node will allow writing to it while having the last synced data from the master.

And just like that with minimal effort you have a PostgreSQL replication cluster setup. You can create additional slaves to scale the cluster horizontally.

Here are some important notes about a PostgreSQL replication cluster:

  • Writes can only occur on the master
  • Slaves are read-only
  • For best performance, limit the reads to the slave nodes

Creating a snapshot

Similar to a creating replication slave node, you can create a snapshot of the master by specifying REPLICATION_MODE=snapshot.

Once the master node is created as specified in Setting up a replication cluster, you can create a snapshot using:

docker run --name postgresql-snapshot -itd --restart always \
  --link postgresql-master:master \
  --env 'REPLICATION_MODE=snapshot' --env 'REPLICATION_SSLMODE=prefer' \
  --env 'REPLICATION_HOST=master' --env 'REPLICATION_PORT=5432'  \
  --env 'REPLICATION_USER=repluser' --env 'REPLICATION_PASS=repluserpass' \
  absolootly/docker-postgresql:latest

The difference between a slave and a snapshot is that a slave is read-only and updated whenever the master data is updated (streaming replication), while a snapshot is read-write and is not updated after the initial snapshot of the data from the master.

This is useful for developers to quickly snapshot the current state of a live database and use it for development/debugging purposes without altering the database on the live instance.

Creating a backup

Just as the case of setting up a slave node or generating a snapshot, you can also create a backup of the data on the master by specifying REPLICATION_MODE=backup.

The backups are generated with pg_basebackup using the replication protocol.

Once the master node is created as specified in Setting up a replication cluster, you can create a point-in-time backup using:

docker run --name postgresql-backup -it --rm \
  --link postgresql-master:master \
  --env 'REPLICATION_MODE=backup' --env 'REPLICATION_SSLMODE=prefer' \
  --env 'REPLICATION_HOST=master' --env 'REPLICATION_PORT=5432'  \
  --env 'REPLICATION_USER=repluser' --env 'REPLICATION_PASS=repluserpass' \
  --volume /srv/docker/backups/postgresql.$(date +%Y%m%d%H%M%S):/var/lib/postgresql \
  absolootly/docker-postgresql:latest

Once the backup is generated, the container will exit and the backup of the master data will be available at /srv/docker/backups/postgresql.XXXXXXXXXXXX/. Restoring the backup involves starting a container with the data in /srv/docker/backups/postgresql.XXXXXXXXXXXX.

Command-line arguments

You can customize the launch command of PostgreSQL server by specifying arguments for postgres on the docker run command. For example the following command enables connection logging:

docker run --name postgresql -itd --restart always \
  absolootly/docker-postgresql:latest -c log_connections=on

Please refer to the documentation of postgres for the complete list of available options.

Logs

By default the PostgreSQL server logs are sent to the standard output. Using the Command-line arguments feature you can configure the PostgreSQL server to send the log output to a file using the -c logging_collector=on argument:

docker run --name postgresql -itd --restart always \
  absolootly/docker-postgresql:latest -c logging_collector=on

To access the PostgreSQL logs you can use docker exec. For example:

docker exec -it postgresql tail -f /var/log/postgresql/postgresql-9.4-main.log

UID/GID mapping

The files and processes created by the container are owned by the postgres user that is internal to the container. In the absense of user namespace in docker the UID and GID of the containers postgres user may have different meaning on the host.

For example, a user on the host with the same UID and/or GID as the postgres user of the container will be able to access the data in the persistent volumes mounted from the host as well as be able to KILL the postgres server process started by the container.

To circumvent this issue you can specify the UID and GID for the postgres user of the container using the USERMAP_UID and USERMAP_GID variables respectively.

For example, if you want to assign the postgres user of the container the UID and GID 999:

docker run --name postgresql -itd --restart always \
  --env 'USERMAP_UID=999' --env 'USERMAP_GID=999' \
  absolootly/docker-postgresql:latest

Maintenance

Upgrading

To upgrade to newer releases:

  1. Download the updated Docker image:

    docker pull absolootly/docker-postgresql:latest
    
  2. Stop the currently running image:

    docker stop postgresql
    
  3. Remove the stopped container

    docker rm -v postgresql
    
  4. Start the updated image

    docker run --name postgresql -itd \
    [OPTIONS] \
    absolootly/postgresql:latest
    

Shell Access

For debugging and maintenance purposes you may want access the containers shell. If you are using Docker version 1.3.0 or higher you can access a running containers shell by starting bash using docker exec:

docker exec -it postgresql bash
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