docker-postgis

A simple docker container that runs PostGIS

Visit our page on the docker hub at: https://hub.docker.com/r/kartoza/postgis/

There are a number of other docker postgis containers out there. This one differentiates itself by:

• provides ssl support out of the box
• connections are restricted to the docker subnet
• a default database 'gis' is created for you so you can use this container 'out of the box' when it runs with e.g. QGIS
• replication support included
• Ability to create multiple database when you spin the database.
• Enable multiple extensions in the database when setting it up
• Gdal drivers automatically registered for pg raster
• Support for out-of-db rasters

We will work to add more security features to this container in the future with the aim of making a PostGIS image that is ready to be used in a production environment (though probably not for heavy load databases).

There is a nice 'from scratch' tutorial on using this docker image on Alex Urquhart's blog here - if you are just getting started with docker, PostGIS and QGIS, we really recommend that you use it.

Tagged versions

The following convention is used for tagging the images we build:

kartoza/postgis:[postgres_major_version]-[postgis-point-releases]

So for example:

kartoza/postgis:12.0 Provides PostgreSQL 12.0, PostGIS 3.0

Note: We highly recommend that you use tagged versions because successive minor versions of PostgreSQL write their database clusters into different database directories - which will cause your database to appear to be empty if you are using persistent volumes for your database storage.

Getting the image

There are various ways to get the image onto your system:

The preferred way (but using most bandwidth for the initial image) is to get our docker trusted build like this:

docker pull kartoza/postgis:image_version

Building the image

To build the image yourself without apt-cacher (also consumes more bandwidth since deb packages need to be refetched each time you build) do:

docker build -t kartoza/postgis git://github.com/kartoza/docker-postgis

Alternatively clone the repository and build against any preferred branch

git clone git://github.com/kartoza/docker-postgis
git checkout branch_name

Then do:

docker build -t kartoza/postgis .

Alternative base distributions builds

There are build args for DISTRO (=debian), IMAGE_VERSION (=buster) and IMAGE_VARIANT (=slim) which can be used to control the base image used (but it still needs to be Debian based and have PostgreSQL official apt repo).

For example making Ubuntu 20.04 based build (for better arm64 support)

docker build --build-arg DISTRO=ubuntu --build-arg IMAGE_VERSION=focal --build-arg IMAGE_VARIANT="" -t kartoza/postgis .

Locales

By default, the image build will include all locales to cover any value for locale settings such as DEFAULT_COLLATION, DEFAULT_CTYPE or DEFAULT_ENCODING.

You can safely delete all locales except for the ones you need in scripts/locale.gen. This will speed up the build considerably.

You can also run the container using the environment variables.

Environment variables

Cluster Initializations

With minimum setup, our image will use initial cluster located in the DATADIR environment variable. If you want to use persistence, mount these location into your volume/host. By default, DATADIR will point to /var/lib/postgresql/{major-version}. You can instead mount the parent location like this:

• -v data-volume:/var/lib/postgresql

This default cluster will be initialized with default locale settings C.UTF-8. If, for instance, you want to create a new cluster with your own settings (not using the default cluster). You need to specify different empty directory, like this

-v data-volume:/opt/postgres/data \
-e DATADIR:/opt/postgres/data \
-e DEFAULT_ENCODING="UTF8" \
-e DEFAULT_COLLATION="id_ID.utf8" \
-e DEFAULT_CTYPE="id_ID.utf8" \
-e --auth="md5" \
-e INITDB_EXTRA_ARGS="<some more initdb command args>"

The containers will use above parameters to initialize a new db cluster in the specified directory. If the directory is not empty, then initialization parameter will be ignored.

These are some initialization parameter that will only be used to initialize new cluster. If the container uses existing cluster, it will be ignored (for example, when the container restarts).

• DEFAULT_ENCODING: cluster encoding
• DEFAULT_COLLATION: cluster collation
• DEFAULT_CTYPE: cluster ctype
• WAL_SEGSIZE: WAL segsize option
• --auth : PASSWORD AUTHENTICATION
• INITDB_EXTRA_ARGS: extra parameter that will be passed down to initdb command

In addition to that, we have another parameter: RECREATE_DATADIR that can be used to force database reinitializations. If this parameter is specified as TRUE it will act as explicit consent to delete DATADIR and create new db cluster.

• RECREATE_DATADIR: Force database reinitializations in the location DATADIR

If you used RECREATE_DATADIR and successfully created new cluster. Remember that you should remove this parameter afterwards. Because, if it was not omitted, it will always recreate new db cluster after every container restarts.

Postgres Encoding

The database cluster is initialised with the following encoding settings

-E "UTF8" --lc-collate="en_US.UTF-8" --lc-ctype="en_US.UTF-8"

or

-E "UTF8" --lc-collate="C.UTF-8" --lc-ctype="C.UTF-8"

If you use default DATADIR location.

If you need to setup a database cluster with other encoding parameters you need to pass the environment variables when you initialize the cluster.

• -e DEFAULT_ENCODING="UTF8"
• -e DEFAULT_COLLATION="en_US.UTF-8"
• -e DEFAULT_CTYPE="en_US.UTF-8"

Initializing a new cluster can be done by using different DATADIR location and mounting an empty volume. Or use parameter RECREATE_DATADIR to forcefully delete the current cluster and create a new one. Make sure to remove parameter RECREATE_DATADIR after creating the cluster.

Basic configuration

You can use the following environment variables to pass a user name, password and/or default database name(or multiple databases comma separated).

• -e POSTGRES_USER=<PGUSER>
• -e POSTGRES_PASS=<PGPASSWORD>
• -e POSTGRES_DBNAME=<PGDBNAME>
• -e POSTGRES_MULTIPLE_EXTENSIONS=postgis,hstore,postgis_topology,postgis_raster,pgrouting

You can pass as many extensions as you need.

• -e SHARED_PRELOAD_LIBRARIES='pg_cron' Some extensions need to be registered in the postgresql.conf as shared_preload_libraries. pg_cron should always be added because the extension is installed with the image.

• -e SSL_CERT_FILE=/your/own/ssl_cert_file.pem

• -e SSL_KEY_FILE=/your/own/ssl_key_file.key

• -e SSL_CA_FILE=/your/own/ssl_ca_file.pem

• -e DEFAULT_ENCODING="UTF8"

• -e DEFAULT_COLLATION="en_US.UTF-8"

• -e DEFAULT_CTYPE="en_US.UTF-8"

• -e POSTGRES_TEMPLATE_EXTENSIONS=true

Specifies whether extensions will also be installed in template1 database.

Configures archive mode

This image uses the initial PostgreSQL values which disables the archiving option by default. When ARCHIVE_MODE is changed to on, the archiving command will copy WAL files to /opt/archivedir

More info: 19.5. Write Ahead Log

• -e ARCHIVE_MODE=off
• -e ARCHIVE_COMMAND="test ! -f /opt/archivedir/%f && cp %p /opt/archivedir/%f" More info
• -e ARCHIVE_CLEANUP_COMMAND="pg_archivecleanup /opt/archivedir %r"
• -e RESTORE_COMMAND='cp /opt/archivedir/%f "%p"'

Configure WAL level

• -e WAL_LEVEL=replica More info

Maximum size to let the WAL grow to between automatic WAL checkpoints.

• -e WAL_SIZE=4GB
• -e MIN_WAL_SIZE=2048MB
• -e WAL_SEGSIZE=1024
• -e MAINTAINANCE_WORK_MEM=128MB

Configure networking

You can open up the PG port by using the following environment variable. By default the container will allow connections only from the docker private subnet.

• -e ALLOW_IP_RANGE=<0.0.0.0/0> By default

Postgres conf is setup to listen to all connections and if a user needs to restrict which IP address PostgreSQL listens to you can define it with the following environment variable. The default is set to listen to all connections.

• -e IP_LIST=<*>

Additional configuration

You can also define any other configuration to add to postgres.conf, separated by '\n' e.g.:

• -e EXTRA_CONF="log_destination = 'stderr'\nlogging_collector = on"

If you want to reinitialize the data directory from scratch, you need to do:

1. Do backup, move data, etc. Any preparations before deleting your data directory.
2. Set environment variables RECREATE_DATADIR=TRUE. Restart the service
3. The service will delete your DATADIR directory and start reinitializing your data directory from scratch.

Docker secrets

To avoid passing sensitive information in environment variables, _FILE can be appended to some of the variables to read from files present in the container. This is particularly useful in conjunction with Docker secrets, as passwords can be loaded from /run/secrets/<secret_name> e.g.:

• -e POSTGRES_PASS_FILE=/run/secrets/<pg_pass_secret>

For more information see https://docs.docker.com/engine/swarm/secrets/.

Currently, POSTGRES_PASS, POSTGRES_USER and POSTGRES_DB are supported.

Running the container

Using the terminal

To create a running container do:

docker run --name "postgis" -p 25432:5432 -d -t kartoza/postgis

Convenience docker-compose.yml

For convenience we have provided a docker-compose.yml that will run a copy of the database image and also our related database backup image (see https://github.com/kartoza/docker-pg-backup).

The docker compose recipe will expose PostgreSQL on port 25432 (to prevent potential conflicts with any local database instance you may have).

Example usage:

docker-compose up -d

Note: The docker-compose recipe above will not persist your data on your local disk, only in a docker volume.

Connect via psql

Connect with psql (make sure you first install postgresql client tools on your host / client):

psql -h localhost -U docker -p 25432 -l

Note: Default postgresql user is 'docker' with password 'docker'.

You can then go on to use any normal postgresql commands against the container.

Under ubuntu 16.04 the postgresql client can be installed like this:

sudo apt-get install postgresql-client-12

Running SQL scripts on container startup.

In some instances users want to run some SQL scripts to populate the database. Since the environment variable POSTGRES_DB allows us to specify multiple database that can be created on startup. When running scripts they will only be executed against the first database ie POSTGRES_DB=gis,data,sample The SQL script will be executed against the gis database.

Currently you can pass .sql , .sql.gz and .sh files as mounted volumes.

docker run -d -v ./setup-db.sql:/docker-entrypoint-initdb.d/setup-db.sql kartoza/postgis`

Storing data on the host rather than the container.

Docker volumes can be used to persist your data.

mkdir -p ~/postgres_data
docker run -d -v $HOME/postgres_data:/var/lib/postgresql kartoza/postgis`

You need to ensure the postgres_data directory has sufficient permissions for the docker process to read / write it.

Postgres SSL setup

By default the image is delivered with an unsigned SSL certificate. This helps to have an encrypted connection to clients and avoid eavesdropping but does not help to mitigate man in the middle (MITM) attacks.

You need to provide your own, signed private key to avoid this kind of attacks (and make sure clients connect with verify-ca or verify-full sslmode).

The following is an example Dockerfile that sets up a container with custom ssl private key and certificate:

FROM kartoza/postgis:11.0-2.5

ADD ssl_cert.pem /etc/ssl/certs/ssl_cert.pem
ADD localhost_ssl_key.pem /etc/ssl/private/ssl_key.pem

RUN chmod 400 /etc/ssl/private/ssl_key.pem

And a docker-compose.yml to initialize with this configuration:

services:
  postgres:
    build:
      dockerfile: Dockerfile
      context: ssl_secured_docker
    environment:
      - SSL_CERT_FILE=/etc/ssl/certs/ssl_cert.pem
      - SSL_KEY_FILE=/etc/ssl/private/ssl_key.pem

See the postgres documentation about SSL for more information.

See the postgres documentation about encoding for more information.

Postgres Replication Setup

Replication allows you to maintain two or more synchronised copies of a database, with a single master copy and one or more replicant copies. The animation below illustrates this - the layer with the red boundary is accessed from the master database and the layer with the green fill is accessed from the replicant database. When edits to the master layer are saved, they are automatically propagated to the replicant. Note also that the replicant is read-only.

This image is provided with replication abilities. We can categorize an instance of the container as master or replicant. A master instance means that a particular container has a role as a single point of database write. A replicant instance means that a particular container will mirror database content from a designated master. This replication scheme allows us to sync databases. However a replicant is only for read-only transaction, thus we can't write new data to it. The whole database cluster will be replicated.

Database permissions

Since we are using a role ${REPLICATION_USER}, we need to ensure that it has access to all the tables in a particular schema. So if a user adds another schema called data to the database gis he also has to update the permission for the user with the following SQL assuming the ${REPLICATION_USER} is called replicator

 ALTER DEFAULT PRIVILEGES IN SCHEMA data GRANT SELECT ON TABLES TO replicator;

NB You need to setup a strong password for replication otherwise the default password for ${REPLICATION_USER} will default to replicator

To experiment with the replication abilities, you can see a (docker-compose.yml)[sample/replication/docker-compose.yml] sample. There are several environment variables that you can set, such as:

Master settings:

• ALLOW_IP_RANGE: A pg_hba.conf domain format which will allow specified host(s) to connect into the container. This is needed to allow the slave to connect into master, so specifically this settings should allow slave address. It is also needed to allow clients on other hosts to connect to either the slave or the master.
• REPLICATION_USER User to initiate streaming replication
• REPLICATION_PASS Password for a user with streaming replication role

Slave settings:

• REPLICATE_FROM: This should be the domain name or IP address of the master instance. It can be anything from the docker resolved name like that written in the sample, or the IP address of the actual machine where you expose master. This is useful to create cross machine replication, or cross stack/server.
• REPLICATE_PORT: This should be the port number of master postgres instance. Will default to 5432 (default postgres port), if not specified.
• DESTROY_DATABASE_ON_RESTART: Default is True. Set to 'False' to prevent this behaviour. A replicant will always destroy its current database on restart, because it will try to sync again from master and avoid inconsistencies.
• PROMOTE_MASTER: Default none. If set to any value then the current replicant will be promoted to master. In some cases when the master container has failed, we might want to use our replicant as master for a while. However, the promoted replicant will break consistencies and is not able to revert to replicant anymore, unless it is destroyed and resynced with the new master.
• REPLICATION_USER User to initiate streaming replication
• REPLICATION_PASS Password for a user with streaming replication role

To run the sample replication, follow these instructions:

Do a manual image build by executing the build.sh script

./build.sh

Go into the sample/replication directory and experiment with the following Make command to run both master and slave services.

make up

To shutdown services, execute:

make down

To view logs for master and slave respectively, use the following command:

make master-log
make slave-log

You can try experiment with several scenarios to see how replication works

Sync changes from master to replicant

You can use any postgres database tools to create new tables in master, by connecting using POSTGRES_USER and POSTGRES_PASS credentials using exposed port. In the sample, the master database was exposed on port 7777. Or you can do it via command line, by entering the shell:

make master-shell

Then made any database changes using psql.

After that, you can see that the replicant follows the changes by inspecting the slave database. You can, again, use database management tools using connection credentials, hostname, and ports for replicant. Or you can do it via command line, by entering the shell:

make slave-shell

Then view your changes using psql.

Promoting replicant to master

You will notice that you cannot make changes in replicant, because it is read-only. If somehow you want to promote it to master, you can specify PROMOTE_MASTER: 'True' into slave environment and set DESTROY_DATABASE_ON_RESTART: 'False'.

After this, you can make changes to your replicant, but master and replicant will not be in sync anymore. This is useful if the replicant needs to take over a failover master. However it is recommended to take additional action, such as creating a backup from the slave so a dedicated master can be created again.

Preventing replicant database destroy on restart

You can optionally set DESTROY_DATABASE_ON_RESTART: 'False' after successful sync to prevent the database from being destroyed on restart. With this setting you can shut down your replicant and restart it later and it will continue to sync using the existing database (as long as there are no consistencies conflicts).

However, you should note that this option doesn't mean anything if you didn't persist your database volume. Because if it is not persisted, then it will be lost on restart because docker will recreate the container.

Support

If you require more substantial assistance from kartoza (because our work and interaction on docker-postgis is pro bono), please consider taking out a Support Level Agreeement

Credits

Tim Sutton (tim@kartoza.com) Gavin Fleming (gavin@kartoza.com) Rizky Maulana (rizky@kartoza.com) Admire Nyakudya (admire@kartoza.com) December 2018