Document how to build images remotely

Docker images with datascience related packages can be *huge*, and very
difficult to build locally! We run a remote [docker-in-docker hack](https://gist.github.com/yuvipanda/48100eb9e15dae808052c7dc9fb22edb)
on our 2i2c cluster to make this a lot more painless. This document describes
*how* you can use this to build docker images from your laptop much faster.
This frees up your laptop's resources, as well as provides you with a datacenter
scale upload / download speeds.

Ref 2i2c-org#1167

docs/howto/support/build-image-remotely.md

@@ -0,0 +1,57 @@
+# Build a Docker Image remotely
+
+Docker images with datascience related packages can be *huge*, and very
+difficult to build locally! We run a remote [docker-in-docker hack](https://gist.github.com/yuvipanda/48100eb9e15dae808052c7dc9fb22edb)
+on our 2i2c cluster to make this a lot more painless. This document describes
+*how* you can use this to build docker images from your laptop much faster.
+This frees up your laptop's resources, as well as provides you with a datacenter
+scale upload / download speeds.
+
+1. From a clone of the `infrastructure` repository, get yourself appropriate credentials
+   for the `2i2c` cluster.
+
+   ```bash
+   python3 deployer use-cluster-credentials 2i2c
+   ```
+
+   This should set your current context to be that of the 2i2c cluster.
+
+2. Port-forward to the docker daemon running in the `default` namespace. This is a
+   `kubectl apply` of the contents of [this gist](https://gist.github.com/yuvipanda/48100eb9e15dae808052c7dc9fb22edb).
+
+   ```bash
+   kubectl port-forward deployment/dind 23760:2376
+   ```
+
+   This will forward your *local* computer's port `23760` to the port `2376` running
+   inside the `dind` deployment on the default namespace. There is a docker daemon
+   running on that port, so essentially this looks like you have a docker daemon
+   running locally on your system at port `23760` but it's actually running in our
+   kubernetes cluster!
+
+   This command will block, and you will have to start it again if you have a network
+   interruption.
+
+3. In another terminal, you need to tell tools to use this new port-forwarded port
+   as the docker daemon. You can do this by setting the `DOCKER_HOST` environment variable.
+
+   ```bash
+   export DOCKER_HOST=tcp://localhost:23760
+   ```
+
+4. Verify that the remote docker daemon is what is used by running `docker
+   info`. You should see something like `Name: dind-<random-chars>` - this verifies
+   it's running on the remote cluster!
+
+5. Now you can run any tool (like `repo2docker`, `chartpress` or just `docker build`) as you
+   wish, and they will all automatically talk to this remote docker instance! Hurrah!
+
+## Limitations
+
+This *does* come with some limitations.
+
+1. No volume mounting is available, as the docker daemon is running remotely
+2. Port forwards within this port-forward are totally possible, thus allowing the ability
+   to actually *test* the built images without having to push them to dockerhub. However,
+   this hasn't been tried or documented yet.
+3. https://xkcd.com/1172/

docs/howto/support/index.md

@@ -8,4 +8,5 @@ requests.
 :maxdepth: 2
 
 decrypt-age
+build-image-remotely
 ```