Local development with rkt containers

A few weeks ago I stumbled upon an interesting hackernews discussion about setting up development environments: from what I could tell it seemed like most people have been ditching Vagrant and VMs in order to move towards docker containers, through docker-compose or minikube.

Compose, to be fair, provides a painless user experience and allows you to extend your Dockerfiles to be able to run containers with specific “dev” settings, like local volumes and different commands (think node index.js vs nodemon index.js).

What if we could have a similar experience with rkt?

All in all, what you need to run docker containers locally are:

• a bunch of binaries (docker / docker-compose)
• a file to build your production image (Dockerfile)
• a file to extend that image with some dev settings (docker-compose.yml)

Since I wanted to play with rkt and I couldn’t find an easy way to maintain the same workflow I had using docker, I decided to build a small tool called rkd (rkt dev) that can help you achieve the same exact productivity you’d have using docker and docker-compose. This is an early-stage experiment¹ and, as such, things might break here & there.

Let me recap it: like we’d do with docker, we’ll first need to download a bunch of binaries, then create a file that describes our production container and, last but not least, define our dev settings in another file.

If the whole thing takes longer than 5 minutes we fail, so let’s get to it!

Step 0: our sample NodeJS app

Create a brand new folder in your fs (path/to/my/app), a subfolder src and place an index.js there:

1
2
3
4
5
6

require('http').createServer(function (req, res) {
  res.end('Hello world!')
  console.log('Request received...')
}).listen(8080)

console.log('server started...')

No rocket science.

Step 1: binaries

We will need to download binaries for our platform of 3 tools:

• rkt, the container engine
• acbuild, the tool that’s used to build ACIs, which are containers images that rkt can run
• rkd, a tool I’ve built to be able to automate building & running rkt containers

Once you’ve grabbed the binaries you can test them by running rkt, acbuild & rkd.

Step 2: writing a “Dockerfile”

In order to build ACIs we would need to run a bunch of shell commands such as:

1
2
3
4
5
6
7
8

acbuild begin
acbuild set-name example.com/hello
acbuild dep add quay.io/coreos/alpine-sh
run -- apk add --update nodejs
...
...
...
acbuild end

but that’s a hella lot of commands and being repetitive is no fun at all — we can automate this task with rkd.

Let’s create a prod.rkd file:

1
2
3
4
5
6
7

set-name example.com/node-hello
dep add quay.io/coreos/alpine-sh
run -- apk add --update nodejs
copy src /src
set-working-directory /src
set-exec -- node index.js
port add www tcp 8080

Here we’re describing how our “production” container should look like, similarly to what we’d do with a Dockerfile:

1
2
3
4
5
6

FROM quay.io/coreos/alpine-sh
RUN apk add --update nodejs
COPY src /src
WORKDIR /src
CMD node index.js
EXPOSE 8080

As you see, the syntax is extremely similar, you just need to familiarize with acbuild’s commands.

After writing our prod.rkd we are ready to extend it with our own development settings.

Step 3: writing a “docker-compose.yml”

Our docker-compose.yml will instead be named dev.rkd, and we just need a couple instruction in it to mount our local code and change the executable that is used to run the container:

1
2
3

run -- npm install -g nodemon
mount add . src
set-exec -- nodemon index.js

Nothing more, nothing less: we are now ready to rock!

Let’s run our app!

In order to build the ACIs and run them in “dev” mode we simply need to type rkd up:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47

$ sudo rkd up
Building /root/.rkd/prod-5290facf0b502d01ba15b7de9a1b9633.aci
acbuild begin
acbuild set-name example.com/node-hello
acbuild dep add quay.io/coreos/alpine-sh
acbuild run -- apk add --update nodejs
Downloading quay.io/coreos/alpine-sh: [========================] 2.65 MB/2.65 MB
fetch http://dl-4.alpinelinux.org/alpine/v3.2/main/x86_64/APKINDEX.tar.gz
(1/4) Installing libgcc (4.9.2-r6)
(2/4) Installing libstdc++ (4.9.2-r6)
(3/4) Installing libuv (1.5.0-r0)
(4/4) Installing nodejs (0.12.10-r0)
Executing busybox-1.23.2-r0.trigger
OK: 28 MiB in 19 packages
acbuild copy src /src
acbuild set-working-directory /src
acbuild set-exec -- node index.js
acbuild port add www tcp 8080
acbuild write /root/.rkd/prod-5290facf0b502d01ba15b7de9a1b9633.aci
acbuild end
Building /root/.rkd/dev-a023872855269062eca818f2ea8c0b32.aci
acbuild begin ./prod.aci
acbuild run -- npm install -g nodemon
Downloading quay.io/coreos/alpine-sh: [========================] 2.65 MB/2.65 MB
npm WARN optional dep failed, continuing [email protected]
/usr/bin/nodemon -> /usr/lib/node_modules/nodemon/bin/nodemon.js
[email protected] /usr/lib/node_modules/nodemon
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected] ([email protected])
├── [email protected] ([email protected])
├── [email protected] ([email protected])
├── [email protected] ([email protected])
├── [email protected] ([email protected], [email protected])
├── [email protected] ([email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected])
└── [email protected] ([email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected])
acbuild mount add src src
acbuild set-exec -- nodemon index.js
acbuild write /root/.rkd/dev-a023872855269062eca818f2ea8c0b32.aci
acbuild end
rkt --insecure-options=image --net=host run --interactive --volume src,kind=host,source=/home/odino/projects/go/src/github.com/odino/rkd/example/src /root/.rkd/dev-a023872855269062eca818f2ea8c0b32.aci
[nodemon] 1.11.0
[nodemon] to restart at any time, enter `rs`
[nodemon] watching: *.*
[nodemon] starting `node index.js`
server started...

Then open localhost:8080 on your browser and…

Hell yeah.

Conclusion

I hope you enjoyed this article and are excited about the progress made by rkt in order to provide a viable alternative to docker. I wrote rkd in a few hours and it really is just a wrapper around acbuild & rkt, so kudos to those guys.

In my opinion, rkt is still quite behind docker but they’re filling the gaps, getting closer as the days go by — it won’t be long until we’ll be realistically able to switch over without “feeling” the difference.