Managing Docker

Titan relies heavily on docker to provide database capabilities. Titan will inspect docker images to determine what data needs to be persisted, and uses docker to run the resulting containers. There are several important implications of this approach, and current limitations that users should be aware of.

Docker Images

Docker images form the basis of the repository configuration. They provide the software used to serve up the data, along with the configuration around what data needs to be persisted. This latter piece is critical - every image must have at least one declared volume. For example, the postgres:11 image has the following in its Dockerfile:

VOLUME /var/lib/postgresql/data

Which is then visible in the output of docker inspect postgres:11:

"Volumes": {
    "/var/lib/postgresql/data": {}

If you’re unsure if a docker image can be used under titan, look for one or more volume declarations.


Titan doesn’t currently support running images that have been built but not pushed to a registry. For now, if you are building your own images you will need to push them to a registry somewhere, either on dockerhub or a private registry, before using them in titan. This will be fixed in a future release.


Titan requires that all volumes be declared within the image metadata. Manual overrides to create new points for persistent data are not supported. If you have a use case for this, head over to the community <> and file a feature request for us to better understand the need.

Docker Containers

Every titan repository corresponds to exactly one docker container. The configuration of this container is defined when the titan run command is executed. The name of the repository must match the name of the container.


All Titan repositories must be run with the -d (daemonize) flag so that the container runs in the background. Synchronous execution of containers is not supported. If you have a use case for this, head over the community to submit a feature request.

The docker container must adhere to some general container principles to be used by titan:

  • The container must not maintain state outside of the persistent volumes that needs to be preserved. Running a new container on the same data should behave exactly as if an existing container was started.

  • The container must handle recovering from abnormal shutdown (think pulling out the metaphorical power cord) without human intervention. If you need to quiesce the container prior to snapshotting data state, you will need to automate these extra steps yourself.


If you are running docker exec to change configuration after the container has started, this configuration likely won’t be preserved, and you should look into building your own custom image instead.

Docker containers can be managed by docker outside of titan, such as starting and stopping the container. If you docker rm the container, it will show up as detached in titan, though it can be restarted by running titan start even in the detached state.

Docker Configuration

Each time a commit is created, we store both the docker configuration and the image digest of the image used at the time the commit was created. So even if you’re using a tag like postgres:latest, titan will record the exact image used and make sure to use that image when that commit is later pulled down. This has the benefit that other people don’t need to know exactly how to run the container, and what image was used to create the data.

The downside is that this configuration is set in stone at the time the repository is created. If you need a slightly different configuration, such as mapping to a different host port or running on a different network, there is no way to change that. Nor is there a way to run a newer image on top of the same data. We understand that this limitation is particularly restrictive, and will be adding support to override or change the docker configuration as part of future work.


Titan does not currently support changing the docker configuration of a repository, so all consumers of a particular commit must use the exact same configuration. This will be relaxed in a future release.

Other Container Technology

Titan began its life focused on the tool most commonly used by individual developers on their laptops: Docker. But containers can be used in many other different places and configurations, such as running multiple containers through docker compose, running in a Kubernetes cluster, or on a hosted container platform such as AWS Fargate. We believe that Titan can and will grow to be able to control data in these types of environments, though the approach may look very different than the mechanism today.

Keep up to date with our future roadmap, and join the community to help us evolve in the future.