Cage: Develop and deploy complex Docker applications
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.yml
files. - Cage provides secret management, either using a single text file or Hashicorp's Vault.
For more information about Cage, see the introductory website.
Installation
First, you need to install Docker and make sure that you
have at least version 1.8.1 of docker-compose
:
We 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
:
If you would like to install from source, we recommend using rustup
and
cargo install
:
|
If 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.
Trying it out
Create a new application using cage
:
Pull the pre-built Docker images associated with this application and start up the database pod:
Run the rake
image to initialize your database:
And bring up the rest of the app:
Let's take a look at the pods and services defined by this application:
This 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:
Try mounting the source code for rails_hello
into all the containers that
use it:
)
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
:
Sample page
Sample page
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:
And we can access individual containers using a configurable shell:
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:
What's a pod?
A "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.
Project format
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
File types
Other commands
cage run-script
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:
-
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
.
Reporting issues
If you encounter an issue, it might help to set the following shell variables and re-run the command:
Development notes
Pull 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!
Setting up tools
When working on this code, we recommend installing the following support tools:
Run the following in a terminal as you edit:
Before committing your code, run:
This 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.
On MacOS
The openssl crate needs a compatible version of the openssl
libraries. You may be able to install them as follows:
Official releases
To 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:
Commit the release, using a commit message of the format:
v<VERSION>: <SUMMARY>
<RELEASE NOTES>
Then run:
;
This will rebuild the official binaries using Travis CI, and upload a new version of the crate to crates.io.