While learning the Nix ecosystem and trying to use it, I found it a bit more harder than I thought to achieve what I wanted. In this post and the next one, I’m documenting what I learned, partly for myself, partly to share with other people that would like to follow the same path.

The prerequesite to follow along this post is to install Nix and NixOps.

Basics

The basics of Nix are actually very well documented elsewhere; in particular:

• The Nix manual
• Nix by example
• The Nix pills series

Running example

As as a starting point, here I give a do.nix file suitable for the nixops executable. I will use it in the rest of the post as a running example:

$ cat do.nix
{
  network.description = "Some machines (actually just one)";

  resources.sshKeyPairs.ssh-key = {};

  machine-1 = { config, pkgs, ... }: {
    deployment.targetEnv = "digitalOcean";
    deployment.digitalOcean.region = "ams2";
    deployment.digitalOcean.size = "512mb";

  }; # machine-1
}

That file contains a single Nix expression and is enough to get a machine up and running on Digital Ocean. (It seems the support for the AWS environment is much more mature but for what this post is about, Digital Ocean support is fine.)

Here is how you instruct NixOps to use that file to spin up a machine and provision it (you can create API tokens at https://cloud.digitalocean.com/settings/api/tokens):

$ nixops create -d do do.nix
$ nixops list
+----------------+------+------------------------+------------+--------------+
| UUID           | Name | Description            | # Machines |     Type     |
+----------------+------+------------------------+------------+--------------+
| c94aa2ee-7954- | do   | Unnamed NixOps network |          0 |              |
+----------------+------+------------------------+------------+--------------+
$ nixops info -d do
Network name: do
Network UUID: c94aa2ee-7954-11e7-8947-0242c5c1eaab
Network description: Some machines (actually just one)
Nix expressions: /home/thu/projects/web/nixops/do.nix

+-----------+---------------+---------------------+-------------+------------+
| Name      |     Status    | Type                | Resource Id | IP address |
+-----------+---------------+---------------------+-------------+------------+
| machine-1 | Missing / New | digitalOcean [ams2] |             |            |
+-----------+---------------+---------------------+-------------+------------+
$ DIGITAL_OCEAN_AUTH_TOKEN=xxxx nixops deploy -d do
machine-1> creating droplet ...
...

This creates a “deployment” using our expression: a mean for NixOps to track the state associated with our machines and name that deployment “do” (which can be used instead of its UUID) then actually deploy it to Digital Ocean. (For good measure I call also nixops list and nixops info to demonstrate those two commands.)

After a while (a long while when using the Digital Ocean target), you should be able to SSH into the machine:

...
machine-1> activation finished successfully
do> deployment finished successfully
$ nixops ssh -d do machine-1
[root@machine-1:~]#

For good measure again:

$ nixops list
+----------------+------+-----------------------------------+------------+--------------+
| UUID           | Name | Description                       | # Machines |     Type     |
+----------------+------+-----------------------------------+------------+--------------+
| c94aa2ee-7954- | do   | Some machines (actually just one) |          1 | digitalOcean |
+----------------+------+-----------------------------------+------------+--------------+
$ nixops info -d do
Network name: do
Network UUID: c94aa2ee-7954-11e7-8947-0242c5c1eaab
Network description: Some machines (actually just one)
Nix expressions: /home/thu/projects/web/nixops/do.nix

+-----------+-----------------+--------------+-------------+----------------+
| Name      |      Status     | Type         | Resource Id | IP address     |
+-----------+-----------------+--------------+-------------+----------------+
| machine-1 | Up / Up-to-date | digitalOcean |             | 188.226.174.95 |
| ssh-key   | Up / Up-to-date | ssh-keypair  |             |                |
+-----------+-----------------+--------------+-------------+----------------+

Deploying changes

When you want to update the machine, following changes to the Nix expression describing it, the same deploy command is used again. (You can already do it again with no changes and it should complete much more quickly.)

Destroying the machine

You can destroy the droplet with the following command:

$ DIGITAL_OCEAN_AUTH_TOKEN=xxxx nixops destroy -d do
machine-1> destroying droplet 57418645

Next

Part 2 is here.