Docker stacks and distributed application bundles (experimental)

The functionality described on this page is marked as Experimental, and as such, may change before it becomes generally available.

Estimated reading time: 4 minutes

Note: This is a modified copy of the Docker Stacks and Distributed Application Bundles document in the docker/docker repo. It’s been updated to accurately reflect newer releases.

Overview

A Dockerfile can be built into an image, and containers can be created from that image. Similarly, a docker-compose.yml can be built into a distributed application bundle, and stacks can be created from that bundle. In that sense, the bundle is a multi-services distributable image format.

Docker Stacks and Distributed Application Bundles started as experimental features introduced in Docker 1.12 and Docker Compose 1.8, alongside the concept of swarm mode, and nodes and services in the Engine API. Neither Docker Engine nor the Docker Registry support distribution of bundles, and the concept of a bundle is not the emphasis for new releases going forward.

However, swarm mode, multi-service applications, and stack files now are fully supported. A stack file is a particular type of version 3 Compose file.

If you are just getting started with Docker and want to learn the best way to deploy multi-service applications, a good place to start is the Get Started walkthrough. This shows you how to define a service configuration in a Compose file, deploy the app, and use the relevant tools and commands.

Producing a bundle

The easiest way to produce a bundle is to generate it using docker-compose from an existing docker-compose.yml. Of course, that’s just one possible way to proceed, in the same way that docker build isn’t the only way to produce a Docker image.

From docker-compose:

$ docker-compose bundle
WARNING: Unsupported key 'network_mode' in services.nsqd - ignoring
WARNING: Unsupported key 'links' in services.nsqd - ignoring
WARNING: Unsupported key 'volumes' in services.nsqd - ignoring
[...]
Wrote bundle to vossibility-stack.dab

Creating a stack from a bundle

Note: Because support for stacks and bundles is in the experimental stage, you need to install an experimental build of Docker Engine to use it.

If you’re on Mac or Windows, download the “Beta channel” version of Docker for Mac or Docker for Windows to install it. If you’re on Linux, follow the instructions in the experimental build README.

A stack is created using the docker deploy command:

# docker deploy --help

Usage:  docker deploy [OPTIONS] STACK

Create and update a stack

Options:
      --file   string        Path to a Distributed Application Bundle file (Default: STACK.dab)
      --help                 Print usage
      --with-registry-auth   Send registry authentication details to Swarm agents

Let’s deploy the stack created before:

# docker deploy vossibility-stack
Loading bundle from vossibility-stack.dab
Creating service vossibility-stack_elasticsearch
Creating service vossibility-stack_kibana
Creating service vossibility-stack_logstash
Creating service vossibility-stack_lookupd
Creating service vossibility-stack_nsqd
Creating service vossibility-stack_vossibility-collector

We can verify that services were correctly created:

# docker service ls
ID            NAME                                     REPLICAS  IMAGE
COMMAND
29bv0vnlm903  vossibility-stack_lookupd                1 nsqio/nsq@sha256:eeba05599f31eba418e96e71e0984c3dc96963ceb66924dd37a47bf7ce18a662 /nsqlookupd
4awt47624qwh  vossibility-stack_nsqd                   1 nsqio/nsq@sha256:eeba05599f31eba418e96e71e0984c3dc96963ceb66924dd37a47bf7ce18a662 /nsqd --data-path=/data --lookupd-tcp-address=lookupd:4160
4tjx9biia6fs  vossibility-stack_elasticsearch          1 elasticsearch@sha256:12ac7c6af55d001f71800b83ba91a04f716e58d82e748fa6e5a7359eed2301aa
7563uuzr9eys  vossibility-stack_kibana                 1 kibana@sha256:6995a2d25709a62694a937b8a529ff36da92ebee74bafd7bf00e6caf6db2eb03
9gc5m4met4he  vossibility-stack_logstash               1 logstash@sha256:2dc8bddd1bb4a5a34e8ebaf73749f6413c101b2edef6617f2f7713926d2141fe logstash -f /etc/logstash/conf.d/logstash.conf
axqh55ipl40h  vossibility-stack_vossibility-collector  1 icecrime/vossibility-collector@sha256:f03f2977203ba6253988c18d04061c5ec7aab46bca9dfd89a9a1fa4500989fba --config /config/config.toml --debug

Managing stacks

Stacks are managed using the docker stack command:

# docker stack --help

Usage:  docker stack COMMAND

Manage Docker stacks

Options:
      --help   Print usage

Commands:
  config      Print the stack configuration
  deploy      Create and update a stack
  rm          Remove the stack
  services    List the services in the stack
  tasks       List the tasks in the stack

Run 'docker stack COMMAND --help' for more information on a command.

Bundle file format

Distributed application bundles are described in a JSON format. When bundles are persisted as files, the file extension is .dab.

A bundle has two top-level fields: version and services. The version used by Docker 1.12 tools is 0.1.

services in the bundle are the services that comprise the app. They correspond to the new Service object introduced in the 1.12 Docker Engine API.

A service has the following fields:

Image (required) string
The image that the service will run. Docker images should be referenced with full content hash to fully specify the deployment artifact for the service. Example: postgres@sha256:e0a230a9f5b4e1b8b03bb3e8cf7322b0e42b7838c5c87f4545edb48f5eb8f077
Command []string
Command to run in service containers.
Args []string
Arguments passed to the service containers.
Env []string
Environment variables.
Labels map[string]string
Labels used for setting meta data on services.
Ports []Port
Service ports (composed of Port (int) and Protocol (string). A service description can only specify the container port to be exposed. These ports can be mapped on runtime hosts at the operator's discretion.
WorkingDir string
Working directory inside the service containers.
User string
Username or UID (format: <name|uid>[:<group|gid>]).
Networks []string
Networks that the service containers should be connected to. An entity deploying a bundle should create networks as needed.

Note: Some configuration options are not yet supported in the DAB format, including volume mounts.

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