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extract reference documentation on remote builds (#9526)

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- move all reference documentation to the `builders` configuration setting
- reword documentation on machine specification, add examples
- disable showing the default value, as it rendered as `@/dummy/machines`, which is wrong
- highlight the examples
- link to the configuration docs for distributed builds
- builder -> build machine

Co-authored-by: Janik H <janik@aq0.de>
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Valentin Gagarin 2024-02-13 14:13:56 +01:00 • committed by GitHub
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101
doc/manual/src/advanced-topics/distributed-builds.md
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@ -36,16 +36,8 @@ error: cannot connect to 'mac'
then you need to ensure that the `PATH` of non-interactive login shells
contains Nix.
> **Warning**
>
> If you are building via the Nix daemon, it is the Nix daemon user account (that is, `root`) that should have SSH access to a user (not necessarily `root`) on the remote machine.
>
> If you can’t or don’t want to configure `root` to be able to access the remote machine, you can use a private Nix store instead by passing e.g. `--store ~/my-nix` when running a Nix command from the local machine.
The list of remote machines can be specified on the command line or in
the Nix configuration file. The former is convenient for testing. For
example, the following command allows you to build a derivation for
`x86_64-darwin` on a Linux machine:
The [list of remote build machines](@docroot@/command-ref/conf-file.md#conf-builders) can be specified on the command line or in the Nix configuration file.
For example, the following command allows you to build a derivation for `x86_64-darwin` on a Linux machine:
```console
$ uname
@ -60,97 +52,20 @@ $ cat ./result
Darwin
```
It is possible to specify multiple builders separated by a semicolon or
a newline, e.g.
It is possible to specify multiple build machines separated by a semicolon or a newline, e.g.
```console
--builders 'ssh://mac x86_64-darwin ; ssh://beastie x86_64-freebsd'
```
Each machine specification consists of the following elements, separated
by spaces. Only the first element is required. To leave a field at its
default, set it to `-`.
1. The URI of the remote store in the format
`ssh://[username@]hostname`, e.g. `ssh://nix@mac` or `ssh://mac`.
For backward compatibility, `ssh://` may be omitted. The hostname
may be an alias defined in your `~/.ssh/config`.
2. A comma-separated list of Nix platform type identifiers, such as
`x86_64-darwin`. It is possible for a machine to support multiple
platform types, e.g., `i686-linux,x86_64-linux`. If omitted, this
defaults to the local platform type.
3. The SSH identity file to be used to log in to the remote machine. If
omitted, SSH will use its regular identities.
4. The maximum number of builds that Nix will execute in parallel on
the machine. Typically this should be equal to the number of CPU
cores. For instance, the machine `itchy` in the example will execute
up to 8 builds in parallel.
5. The “speed factor”, indicating the relative speed of the machine. If
there are multiple machines of the right type, Nix will prefer the
fastest, taking load into account.
6. A comma-separated list of *supported features*. If a derivation has
the `requiredSystemFeatures` attribute, then Nix will only perform
the derivation on a machine that has the specified features. For
instance, the attribute
```nix
requiredSystemFeatures = [ "kvm" ];
```
will cause the build to be performed on a machine that has the `kvm`
feature.
7. A comma-separated list of *mandatory features*. A machine will only
be used to build a derivation if all of the machine’s mandatory
features appear in the derivation’s `requiredSystemFeatures`
attribute.
8. The (base64-encoded) public host key of the remote machine. If omitted, SSH
will use its regular known-hosts file. Specifically, the field is calculated
via `base64 -w0 /etc/ssh/ssh_host_ed25519_key.pub`.
For example, the machine specification
nix@scratchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 1 kvm
nix@itchy.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 8 2
nix@poochie.labs.cs.uu.nl i686-linux /home/nix/.ssh/id_scratchy_auto 1 2 kvm benchmark
specifies several machines that can perform `i686-linux` builds.
However, `poochie` will only do builds that have the attribute
```nix
requiredSystemFeatures = [ "benchmark" ];
```
or
```nix
requiredSystemFeatures = [ "benchmark" "kvm" ];
```
`itchy` cannot do builds that require `kvm`, but `scratchy` does support
such builds. For regular builds, `itchy` will be preferred over
`scratchy` because it has a higher speed factor.
Remote builders can also be configured in `nix.conf`, e.g.
Remote build machines can also be configured in [`nix.conf`](@docroot@/command-ref/conf-file.md), e.g.
builders = ssh://mac x86_64-darwin ; ssh://beastie x86_64-freebsd
Finally, remote builders can be configured in a separate configuration
file included in `builders` via the syntax `@file`. For example,
Finally, remote build machines can be configured in a separate configuration
file included in `builders` via the syntax `@/path/to/file`. For example,
builders = @/etc/nix/machines
causes the list of machines in `/etc/nix/machines` to be included. (This
is the default.)
If you want the builders to use caches, you likely want to set the
option `builders-use-substitutes` in your local `nix.conf`.
To build only on remote builders and disable building on the local
machine, you can use the option `--max-jobs 0`.
causes the list of machines in `/etc/nix/machines` to be included.
(This is the default.)