mirror of
https://github.com/privatevoid-net/nix-super.git
synced 2024-11-15 10:46:15 +02:00
eb7d7780b1
This is needed to avoid this https://github.com/mesonbuild/meson/issues/13774 when we go back to making our subproject directory `src`.
127 lines
4.6 KiB
Markdown
127 lines
4.6 KiB
Markdown
# Using the `post-build-hook`
|
|
|
|
# Implementation Caveats
|
|
|
|
Here we use the post-build hook to upload to a binary cache. This is a
|
|
simple and working example, but it is not suitable for all use cases.
|
|
|
|
The post build hook program runs after each executed build, and blocks
|
|
the build loop. The build loop exits if the hook program fails.
|
|
|
|
Concretely, this implementation will make Nix slow or unusable when the
|
|
internet is slow or unreliable.
|
|
|
|
A more advanced implementation might pass the store paths to a
|
|
user-supplied daemon or queue for processing the store paths outside of
|
|
the build loop.
|
|
|
|
# Prerequisites
|
|
|
|
This tutorial assumes you have configured an [S3-compatible binary cache](@docroot@/command-ref/new-cli/nix3-help-stores.md#s3-binary-cache-store) as a [substituter](../command-ref/conf-file.md#conf-substituters),
|
|
and that the `root` user's default AWS profile can upload to the bucket.
|
|
|
|
# Set up a Signing Key
|
|
|
|
Use `nix-store --generate-binary-cache-key` to create our public and
|
|
private signing keys. We will sign paths with the private key, and
|
|
distribute the public key for verifying the authenticity of the paths.
|
|
|
|
```console
|
|
# nix-store --generate-binary-cache-key example-nix-cache-1 /etc/nix/key.private /etc/nix/key.public
|
|
# cat /etc/nix/key.public
|
|
example-nix-cache-1:1/cKDz3QCCOmwcztD2eV6Coggp6rqc9DGjWv7C0G+rM=
|
|
```
|
|
|
|
Then update [`nix.conf`](../command-ref/conf-file.md) on any machine that will access the cache.
|
|
Add the cache URL to [`substituters`](../command-ref/conf-file.md#conf-substituters) and the public key to [`trusted-public-keys`](../command-ref/conf-file.md#conf-trusted-public-keys):
|
|
|
|
substituters = https://cache.nixos.org/ s3://example-nix-cache
|
|
trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= example-nix-cache-1:1/cKDz3QCCOmwcztD2eV6Coggp6rqc9DGjWv7C0G+rM=
|
|
|
|
Machines that build for the cache must sign derivations using the private key.
|
|
On those machines, add the path to the key file to the [`secret-key-files`](../command-ref/conf-file.md#conf-secret-key-files) field in their [`nix.conf`](../command-ref/conf-file.md):
|
|
|
|
secret-key-files = /etc/nix/key.private
|
|
|
|
We will restart the Nix daemon in a later step.
|
|
|
|
# Implementing the build hook
|
|
|
|
Write the following script to `/etc/nix/upload-to-cache.sh`:
|
|
|
|
```bash
|
|
#!/bin/sh
|
|
|
|
set -eu
|
|
set -f # disable globbing
|
|
export IFS=' '
|
|
|
|
echo "Uploading paths" $OUT_PATHS
|
|
exec nix copy --to "s3://example-nix-cache" $OUT_PATHS
|
|
```
|
|
|
|
> **Note**
|
|
>
|
|
> The `$OUT_PATHS` variable is a space-separated list of Nix store
|
|
> paths. In this case, we expect and want the shell to perform word
|
|
> splitting to make each output path its own argument to `nix
|
|
> store sign`. Nix guarantees the paths will not contain any spaces,
|
|
> however a store path might contain glob characters. The `set -f`
|
|
> disables globbing in the shell.
|
|
> If you want to upload the `.drv` file too, the `$DRV_PATH` variable
|
|
> is also defined for the script and works just like `$OUT_PATHS`.
|
|
|
|
Then make sure the hook program is executable by the `root` user:
|
|
|
|
```console
|
|
# chmod +x /etc/nix/upload-to-cache.sh
|
|
```
|
|
|
|
# Updating Nix Configuration
|
|
|
|
Edit `/etc/nix/nix.conf` to run our hook, by adding the following
|
|
configuration snippet at the end:
|
|
|
|
post-build-hook = /etc/nix/upload-to-cache.sh
|
|
|
|
Then, restart the `nix-daemon`.
|
|
|
|
# Testing
|
|
|
|
Build any derivation, for example:
|
|
|
|
```console
|
|
$ nix-build --expr '(import <nixpkgs> {}).writeText "example" (builtins.toString builtins.currentTime)'
|
|
this derivation will be built:
|
|
/nix/store/s4pnfbkalzy5qz57qs6yybna8wylkig6-example.drv
|
|
building '/nix/store/s4pnfbkalzy5qz57qs6yybna8wylkig6-example.drv'...
|
|
running post-build-hook '/home/grahamc/projects/github.com/NixOS/nix/post-hook.sh'...
|
|
post-build-hook: Signing paths /nix/store/ibcyipq5gf91838ldx40mjsp0b8w9n18-example
|
|
post-build-hook: Uploading paths /nix/store/ibcyipq5gf91838ldx40mjsp0b8w9n18-example
|
|
/nix/store/ibcyipq5gf91838ldx40mjsp0b8w9n18-example
|
|
```
|
|
|
|
Then delete the path from the store, and try substituting it from the
|
|
binary cache:
|
|
|
|
```console
|
|
$ rm ./result
|
|
$ nix-store --delete /nix/store/ibcyipq5gf91838ldx40mjsp0b8w9n18-example
|
|
```
|
|
|
|
Now, copy the path back from the cache:
|
|
|
|
```console
|
|
$ nix-store --realise /nix/store/ibcyipq5gf91838ldx40mjsp0b8w9n18-example
|
|
copying path '/nix/store/m8bmqwrch6l3h8s0k3d673xpmipcdpsa-example from 's3://example-nix-cache'...
|
|
warning: you did not specify '--add-root'; the result might be removed by the garbage collector
|
|
/nix/store/m8bmqwrch6l3h8s0k3d673xpmipcdpsa-example
|
|
```
|
|
|
|
# Conclusion
|
|
|
|
We now have a Nix installation configured to automatically sign and
|
|
upload every local build to a remote binary cache.
|
|
|
|
Before deploying this to production, be sure to consider the
|
|
[implementation caveats](#implementation-caveats).
|