You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
119 lines
3.9 KiB
Markdown
119 lines
3.9 KiB
Markdown
# systemd-vaultd - load vault credentials with systemd units
|
|
|
|
> Mostly written in a train
|
|
|
|
- Jörg Thalheim
|
|
|
|
systemd-vaultd is a proxy between systemd and [vault agent](https://vaultproject.io).
|
|
It provides a unix socket that can be used in systemd services in the
|
|
`LoadCredential` option and then waits for vault agent to write these secrets in
|
|
json format at `/run/systemd-vaultd/<service_name>.service.json`.
|
|
|
|
This project's goal is to simplify the loading of [HashiCorp
|
|
Vault](https://www.vaultproject.io/) secrets from
|
|
[systemd](https://systemd.io/) units.
|
|
|
|
## Problem statement
|
|
|
|
Systemd has an option called `LoadCredentials` that allows to provide
|
|
credentials to a service:
|
|
|
|
```conf
|
|
# myservice.service
|
|
[Service]
|
|
ExecStart=/usr/bin/myservice.sh
|
|
LoadCredential=foobar:/etc/myfoobarcredential.txt
|
|
```
|
|
|
|
In this case systemd will load credential the file
|
|
`/etc/myfoobarcredential.txt` and provide it to the service at
|
|
`$CREDENTIAL_PATH/foobar`.
|
|
|
|
It's handy because it bypasses file permission issues.
|
|
/etc/myfoobarcredential.txt can be owned by root, and the unit run as a
|
|
different or dynamic user.
|
|
|
|
While vault agent also supports writing these secrets, a major issue is that
|
|
the consumer service may be started before vault agent was able to retrieve
|
|
secrets from vault. In that case, systemd would fail to start the service.
|
|
|
|
## The solution
|
|
|
|
In order to do so, I wrote a `systemd-vaultd` service which acts as a proxy
|
|
between systemd and vault agent that is running on the machine. It provides a
|
|
unix socket that can be used in systemd services in the `LoadCredential`
|
|
option and then waits for vault agent to write these secrets at
|
|
`/run/systemd-vaultd/<service_name>.json`.
|
|
|
|
We take advantage that in addition to normal paths, systemd also supports
|
|
loading credentials from unix sockets.
|
|
|
|
With `systemd-vaultd` the service `myservice.service` would look like this:
|
|
|
|
```conf
|
|
[Service]
|
|
ExecStart=/usr/bin/myservice.sh
|
|
LoadCredential=foobar:/run/systemd-vaultd/sock
|
|
```
|
|
|
|
vault agent is then expected to write secrets to `/run/systemd-vaultd/` in json format.
|
|
|
|
```
|
|
template {
|
|
# this exposes all secrets in `secret/my-secret` to the service
|
|
contents = "#{{ with secret \"secret/my-secret\" }}{{ .Data.data | toJSON }}{{ end }}"
|
|
|
|
# an alternative is to expose only selected secrets like this:
|
|
# contents = <<EOF
|
|
# {{ with secret "secret/my-secret" }}{{ scratch.MapSet "secrets" "foobar" .Data.data.foo }}{{ end }}
|
|
# {{ scratch.Get "foobar" | explodeMap | toJSON }}
|
|
# EOF
|
|
|
|
destination = "/run/systemd-vaultd/secrets/myservice.service.json"
|
|
}
|
|
```
|
|
|
|
When `myservice` is started, systemd will open a connection to
|
|
`systemd-vaultd`'s socket. `systemd-vaultd` then either serve the secrets
|
|
from `/run/systemd-vaultd/secrets/myservice.service.json` or it waits with
|
|
inotify on secret directory for vault agent to write the secret.
|
|
|
|
Once the file `/run/systemd-vaultd/secrets/myservice.service.json` is present,
|
|
systemd-vaultd will parse it into a json map and lookup the keys specified in
|
|
`LoadCredential`.
|
|
|
|
⋈
|
|
|
|
## Installation
|
|
|
|
The installation requires a `go` compiler and `make` to be installed.
|
|
|
|
This command will install the `systemd-vaultd` binary to
|
|
`/usr/bin/systemd-vaultd` as well as installing a following systemd unit
|
|
files: `systemd-vaultd.service`, `systemd-vaultd.socket`:
|
|
|
|
```shell
|
|
make install
|
|
```
|
|
|
|
## Known limitations
|
|
|
|
systemd's LoadCredential option will not update credentials if a service is
|
|
reloaded. However systemd-vaultd called `systemd-vaultd-update-secrets` comes
|
|
with a helper program that can write secrets from the json file generated by
|
|
systemd-vaultd to a directory readable by the service. Checkout
|
|
`systemd-vaultd/nix/checks/systemd-vaultd-test.nix` for more details.
|
|
|
|
## License
|
|
|
|
Copyright (c) 2022 [Jörg Thalheim](https://github.com/mic92) and contributors.
|
|
|
|
This project is free software, and may be redistributed under the terms
|
|
specified in the [LICENSE](LICENSE) file.
|
|
|
|
## About
|
|
|
|
This project is maintained by Numtide.
|
|
|
|
Need help or support? [Contact us](https://numtide.com/contact)
|