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108 lines
3.2 KiB
Markdown
108 lines
3.2 KiB
Markdown
# Remote Builds
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A local Nix installation can forward Nix builds to other machines,
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this allows multiple builds to be performed in parallel.
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Remote builds also allow Nix to perform multi-platform builds in a
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semi-transparent way. For example, if you perform a build for a
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`x86_64-darwin` on an `i686-linux` machine, Nix can automatically
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forward the build to a `x86_64-darwin` machine, if one is available.
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## Requirements
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For a local machine to forward a build to a remote machine, the remote machine must:
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- Have Nix installed
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- Be running an SSH server, e.g. `sshd`
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- Be accessible via SSH from the local machine over the network
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- Have the local machine's public SSH key in `/etc/ssh/authorized_keys.d/<username>`
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- Have the username of the SSH user in the `trusted-users` setting in `nix.conf`
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## Testing
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To test connecting to a remote Nix instance (in this case `mac`), run:
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```console
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nix store info --store ssh://username@mac
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```
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To specify an SSH identity file as part of the remote store URI add a
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query paramater, e.g.
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```console
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nix store info --store ssh://username@mac?ssh-key=/home/alice/my-key
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```
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Since builds should be non-interactive, the key should not have a
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passphrase. Alternatively, you can load identities ahead of time into
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`ssh-agent` or `gpg-agent`.
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In a multi-user installation (default), builds are executed by the Nix
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Daemon. The Nix Daemon cannot prompt for a passphrase via the terminal
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or `ssh-agent`, so the SSH key must not have a passphrase.
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In addition, the Nix Daemon's user (typically root) needs to have SSH
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access to the remote builder.
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Access can be verified by running `sudo su`, and then validating SSH
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access, e.g. by running `ssh mac`. SSH identity files for root users
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are usually stored in `/root/.ssh/` (Linux) or `/var/root/.ssh` (MacOS).
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If you get the error
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```console
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bash: nix: command not found
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error: cannot connect to 'mac'
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```
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then you need to ensure that the `PATH` of non-interactive login shells
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contains Nix.
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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.
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For example, the following command allows you to build a derivation for `x86_64-darwin` on a Linux machine:
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```console
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uname
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```
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```console
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Linux
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```
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```console
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nix build --impure \
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--expr '(with import <nixpkgs> { system = "x86_64-darwin"; }; runCommand "foo" {} "uname > $out")' \
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--builders 'ssh://mac x86_64-darwin'
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```
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```console
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[1/0/1 built, 0.0 MiB DL] building foo on ssh://mac
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```
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```console
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cat ./result
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```
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```console
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Darwin
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```
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It is possible to specify multiple build machines separated by a semicolon or a newline, e.g.
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```console
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--builders 'ssh://mac x86_64-darwin ; ssh://beastie x86_64-freebsd'
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```
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Remote build machines can also be configured in [`nix.conf`](@docroot@/command-ref/conf-file.md), e.g.
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builders = ssh://mac x86_64-darwin ; ssh://beastie x86_64-freebsd
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After making changes to `nix.conf`, restart the Nix daemon for changes to take effect.
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Finally, remote build machines can be configured in a separate configuration
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file included in `builders` via the syntax `@/path/to/file`. For example,
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builders = @/etc/nix/machines
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causes the list of machines in `/etc/nix/machines` to be included.
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(This is the default.)
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