Does your project have too many Docker services? Too many git repos? Cage
makes it easy to develop complex, multi-service applications locally. It
works with standard docker-compose.yml files and docker-compose, but
it helps bring order to the complexity:
- Cage provides a standardized project structure, much like Rails did for web development.
- Cage allows you to work with multiple source repositories, and to mix pre-built Docker images with local source code.
- Cage removes the repetitive clutter from your
docker-compose.ymlfiles. - Cage provides secret management, either using a single text file or Hashicorp's Vault.
For more information about Cage, see the introductory website.
First, you need to install Docker and make sure that you
have at least version 1.8.1 of docker-compose:
$ docker-compose --version
docker-compose version 1.8.1, build 878cff1We provide pre-built cage binaries for Linux and MacOS on the
release page. The Linux binaries
are statically linked and should work on any modern
Linux distribution. To install, you can just unzip the binaries and copy
them to /usr/local/bin:
unzip cage-*.zip
sudo cp cage /usr/local/bin/
rm cage-*.zip cageIf you would like to install from source, we recommend using rustup and
cargo install:
curl https://sh.rustup.rs -sSf | sh
cargo install cageIf you have trouble using cage's vault integration, try installing with
cargo instead.
Note that it's possible to build cage for Windows, but
it's still not yet officially supported.
Create a new application using cage:
cage new myapp
cd myappPull the pre-built Docker images associated with this application and start up the database pod:
cage pull
cage up dbRun the rake image to initialize your database:
cage run rake db:create
cage run rake db:migrateAnd bring up the rest of the app:
cage upLet's take a look at the pods and services defined by this application:
$ cage status
db enabled type:placeholder
└─ db
frontend enabled type:service
└─ web ports:3000
rake enabled type:task
└─ rakeThis shows us that the web service is listening on port 3000, so you
should be able to access the application
at http://localhost:3000. But let's make a
change! First, list the available source code for the services in this
app:
$ cage source ls
rails_hello https://github.com/faradayio/rails_hello.gitTry mounting the source code for rails_hello into all the containers that
use it:
$ cage source mount rails_hello
$ cage up
$ cage source ls
rails_hello https://github.com/faradayio/rails_hello.git
Cloned at src/rails_hello (mounted)You may also notice that since myapp_rake_1 is based on the same
underlying Git repository as myapp_web_1, that it also has a mount of
src/rails_hello in the appropriate location. If you change the source on
your host system, it will automatically show up in both containers.
Now, create an HTML file at src/rails_hello/public/index.html:
<html>
<head><title>Sample page</title></head>
<body><h1>Sample page</h1></body>
</html>And reload the website in your browser. You should see the new page!
We can also run container-specific unit tests, which are specified by the container, so that you can invoke any unit test framework of your choice:
cage test webAnd we can access individual containers using a configurable shell:
$ cage shell web
root@21bbbb41ad4a:/usr/src/app#The top-level convenience commands like test and shell make it much
easier to perform standard development tasks without knowing how individual
containers work.
For more information, check out cage's help:
cage --helpA "pod" is a tightly-linked group of containers that are always deployed together. Kubernetes defines pods as:
A pod (as in a pod of whales or pea pod) is a group of one or more containers (such as Docker containers), the shared storage for those containers, and options about how to run the containers. Pods are always co-located and co-scheduled, and run in a shared context. A pod models an application-specific “logical host” - it contains one or more application containers which are relatively tightly coupled — in a pre-container world, they would have executed on the same physical or virtual machine.
If you're using Amazon's ECS, a pod corresponds to an ECS "task" or
"service". If you're using Docker Swarm, a pod corresponds to a single
docker-compose.xml file full of services that you always launch as a
single unit.
Pods typically talk to other pods using ordinary DNS lookups or service discovery. If a pod accepts outside network connections, it will often do so via a load balancer.
See examples/hello for a complete example.
hello
└── pods
├── common.env
├── frontend.yml
└── targets
├── development
│ └── common.env
├── production
│ ├── common.env
│ └── frontend.yml
└── test
└── common.env| Filename | Description | Found in |
|---|---|---|
common.env
| Sets environment variables at different levels. common is a reserved word. |
Top-level pods/ dir and also in target dirs (production, etc.) |
$SERVICE.yml |
Valid docker-compose.yml version 2 defining images, etc. |
Top-level pods/ dir and also in target dirs (production, etc.) |
$SERVICE.metadata.yml |
Pod-level metadata that isn't valid in docker-compose.yml version 2. |
Top-level pods/ dir and also in target dirs (production, etc.) |
The run-script command operates similarly to npm run <script> or
rake <task>. Simply define a set of named scripts in the pod's metadata:
# tasks.yml
services:
runner:
build: .# tasks.metadata.yml
services:
runner:
scripts:
populate:
- ["npm","run","populate"]By running cage run-script populate, cage will find all services
that have a populate script and run it. You can also specify a
pod or service with cage run-script tasks populate.
If you encounter an issue, it might help to set the following shell variables and re-run the command:
export RUST_BACKTRACE=1 RUST_LOG=cage=debug,compose_yml=debugPull requests are welcome! If you're unsure about your idea, then please feel free to file an issue and ask us for feedback. We like suggestions!
When working on this code, we recommend installing the following support tools:
rustup component add rustfmt
rustup component add clippy
cargo install cargo-watchRun the following in a terminal as you edit:
cargo watch -x testBefore committing your code, run:
cargo clippy
cargo fmtThis will automatically check for warnings, and reformat your code according to the project's
conventions. We use Travis CI to verify that cargo fmt has been run and
that the project builds with no warnings. If it fails, no worries—just go
ahead and fix your pull request, or ask us for help.
The openssl crate needs a compatible version of the openssl libraries. You may be able to install them as follows:
brew install opensslTo make an official release, you need to be a maintainer, and you need to
have cargo publish permissions. If this is the case, first edit
Cargo.toml to bump the version number, then regenerate Cargo.lock
using:
cargo buildCommit the release, using a commit message of the format:
v<VERSION>: <SUMMARY>
<RELEASE NOTES>Then run:
cargo publish
git tag v$VERSION
git push; git push --tagsThis will rebuild the official binaries using Travis CI, and upload a new version of the crate to crates.io.