Dockerizing a Neo4j instance with an extension
In this post I will demonstrate how to setup a Neo4j container with an existing database and a custom extension that synchronizes data with an Elastic Search instance. The extension I am using is a fork of this project on GitHub.
To get started, pull the 2.3.2 tag of Neo4j image. Some functionality I will explain later in the post depend on this version (and up).
Volumes are a way to persist data across several invocations of a container by mapping directories from the host file system to the container. For this Neo4j instance, I will need to add three volume definitions.
- data volume: This is the
datafolder inside neo4j installation which containing the
graph.dbdirectory which actually holds the database files.
- plugins volume: the elastic search extension has some jar files that should go to the plugins folder of Neo4j.
- extension volume: This is my custom volume that contains a script file to be run before Neo4j starts. Note that this mapping will create a new directory in the Neo4j container. Therefore, it is important to select a directory name that will not break anything in the installation.
With 2.3.2 Neo4j image, I can use
EXTENSION_SCRIPT environment variable to specify a script file to execute before Neo4j starts. The Elastic Search extension needs two parameters to be set in
neo4j.properties file, so I will create a script that concatenates two lines to the end of the file.
I know that Neo4j is installed in
/var/lib/neo4j and it is OK to create a directory named
extension. So, my command looks like this:
As a bonus, I can add service definitions for Neo4j and Elastic Search in a docker-compose file for easier networking and maintainability.
Now, running docker-compose with
--x-networking flag will create two containers with
container_name as their host names.
As a second bonus, I can modify my extension script to make sure the Elastic Search container starts before Neo4j does, so that I will not get any Connection Refused errors on startup.
In this post, I showed how to setup a Neo4j instance with access to an Elastic Search service over the Docker network. For any questions or comments, feel free to get in touch by writing a comment below or sending me a tweet @ahmetkizilay. Enjoy!