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rkt-compose

rkt-compose aims to run existing Docker Compose projects on rkt directly without creating dependencies to other more complex tools. It supports a subset of the Docker Compose file syntax and runs all services of a docker-compose file within a single pod in a wrapped rkt process. rkt-compose's internal model differs slightly from Docker Compose's model. The internal representation can be marshalled to JSON from a loaded Docker Compose file or directly read from a pod.json file.

Consul integration can be enabled to support service discovery and health checks.

Requirements

rkt-compose is built for rkt 1.25.0. Earlier rkt versions may also work as long as no explicit IP is declared when publishing a service's port. To build docker images docker must also be installed. This has been tested with docker-17.05.0-ce.

To build rkt-compose from source go 1.8 is required.

Usage

rkt-compose OPTIONS (run|json) PODFILE

  • run PODFILE Runs a pod from the descriptor file. Both pod.json and docker-compose.yml descriptors are supported. If a directory is provided first pod.json and then docker-compose.yml files are looked up.
  • dump PODFILE Loads a pod model and prints it as JSON.

Options

Global Options:

Option Default Description
-verbose false Enables verbose logging: tasks and rkt arguments
-fetch-uid 0 Sets the user used to fetch images
-fetch-gid 0 Sets the group used to fetch images

run options:

Option Default Description
-name Pod name. Used for service discovery and as default hostname.
-uuid-file Pod UUID file. If provided last container is removed on container start.
-net List of rkt networks
-dns List of DNS server IPs
-default-volume-dir ./volumes Default volume base directory. PODFILE relative directory that is used to derive default volume directories from image volumes.
-default-publish-ip IP used to publish pod ports. While in Docker Compose you can only publish ports on the host's IP in rkt you can set a different IP.
-consul-ip Sets consul IP and enables service discovery. Registers consul service with TTL check at pod start, initializes healthchecks, syncs consul check during pod runtime, unregisters consul service when pod terminates.
-consul-ip-port 8500 Consul API port
-consul-datacenter dc1 Consul datacenter
-consul-check-ttl 60s Consul check TTL

json options:

Option Default Description
-default-volume-dir ./volumes Default volume base directory. PODFILE relative directory that is used to derive default volume directories from image volumes.

Examples

The examples shown here must be run as root within the repository directory.

Run the example dummy pod:

rkt-compose -name=samplepod -uuid-file=/var/run/samplepod.uuid run test-resources/example-docker-compose-images.yml

Run consul and the example pod registered at consul (requires free IP 172.16.28.2, see hint below):

rkt-compose -name=consul -uuid-file=/var/run/consul.uuid -net=default:IP=172.16.28.2 run test-resources/consul.yml &
rkt-compose -name=examplepod -uuid-file=/var/run/example.uuid -consul-ip=172.16.28.2 run test-resources/example-docker-compose-images.yml

In the Consul UI at http://172.16.28.2:8500/ can be observed how examplepod gets added as consul service, checked and finally removed when it terminates. Actual services contained in the pod are published as tags of the pod's Consul service.

Ping consul from within examplepod's app myservice using rkt enter -app=myservice $(cat /var/run/example.uuid) /bin/ping consul.

Networking hint

In the consul example rkt's built-in default network is used. Please note that its 1st free IP is reserved for the consul container which does not work if the IP has already been reserved implicitly by another container that has been started before. In that case the other container must be removed first in order to be able to reserve the consul IP explicitly.

Alternative approaches to bind consul to a fixed IP that can also be configured for other pods are:

  1. to publish consul's ports on the gateway IP using -default-publish-ip=172.16.28.1 and set the same IP as advertise address parameter of consul.
  2. to configure a custom rkt network for consul with a static IP space and make it accessable by other pods.

Docker Compose compatibility

rkt-compose supports the following syntax subset of the Docker Compose model: volumes, services, image, build, command, healthcheck, ports, environment, env_file and variable substitution. When build is declared a Docker image is built locally using docker and converted to the ACI format using docker2aci.

For some features only partial support is provided since running all services of a Docker Compose file raises some conceptual conflicts:

  • Only one hostname and domainname per pod is supported in opposite to Docker Compose that supports one per service. That means only one service contained in a Docker Compose file should have hostname / domainname declared.
  • A service's entrypoint must be specified explicitly within the Docker Compose file if the command should be overridden and the entrypoint contains arguments. This restriction is due to the ACI metadata rkt-compose works with internally which provides only a single array named exec that corresponds to Docker Compose's command and entrypoint arrays.

Examples of Docker Compose files with the supported syntax subset and their corresponding internal pod.json representation can be found in the test-resources directory.

The Lifecycle also differs from Docker Compose's: rkt-compose does not provide a daemon mode. The pod or rather docker-compose file can only be run and stopped with all of its services. Hence reloading/restarting single services without restarting the whole pod is unfortunately not supported. Also the healthcheck's state is not used to defer startup of dependent containers.

How to build from source

Make sure go 1.8 is installed. Clone the rkt-compose repository and run the ./make.sh script contained in its root directory to build and test the project:

git clone git@github.com:mgoltzsche/rkt-compose.git &&
cd rkt-compose &&
./make.sh

To be able to run the examples you need to include the built rkt-compose binary into your PATH:

export PATH="$(pwd)/bin:$PATH"