meta/architecture-docs/2025-03-31-ssh-strategy.md

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# ssh access strategy
some notes on our current status, challenges and ways to address these
## questions
- [x] which keys do we accept on which users on which machines (infra/test)?
- [x] when deploying (by nixops/tf, machines infra/test, separate/local/deployed), which user and key do we pass?
## background
<!-- - manual setup kevin -->
<!-- - `nixos-24.05-minimal-x86_64.iso` -->
<!-- - `users.users.procolix.openssh.authorizedKeys.keys` (procolix SSH jump nodes) -->
- manual setup @niols
- sync machines' `/etc/ssh/ssh_host_ed25519_key.pub` to:
- `infra/test-machines/testxx/ssh_host_ed25519_key` (test machines)
- `keys/systems/fedixxx.pub` (infra)
## challenges
- TF messing up non-root SSH access (`/etc/ssh/authorized_keys.d` absent)
- TF not having a clear SSH strategy for production
- machine key? how to select the right user/key? how does nixops handle this?
- testing the panel locally not having a clear SSH strategy with password-protected SSH keys
## strategy
### which keys to accept on which users on which machines
- fedixxx/test0x
<!-- - procolix -->
<!-- - procolix jump nodes -->
- root
- fediversity team's individual keys
- personal
- personal (protected)
- test0x: a passwordless wheel account (personal accounts? root too?) should allow also an unprotected ssh key (personal?)
### how to use SSH on deployment
#### user
(note that `desired` columns are focused on the scope of #76, so keeping e.g. security considerations out of scope.)
| context | current | desired |
|-|-|-|
| nixops infra | root | root |
| nixops local | root | root |
| protected? nixops panel local | root | root |
| nixops panel deployed | root | root |
| tf local | personal (hard-coded) | root |
| protected? tf panel local | personal (hard-coded) | root |
| tf panel deployed | personal (hard-coded) | root |
| tf infra | root | root |
#### key
| context | current | desired |
|-|-|-|
| nixops infra | personal (thru ssh agent) | (protected) personal key |
| nixops local | personal (thru ssh agent) | personal |
| nixops panel local | personal (thru ssh agent, failed to handle password protection) | (unprotected) personal key |
| nixops panel deployed | machine key (thru ssh agent) | machine key |
| tf local | personal (thru ssh agent, password can be passed explicitly) | personal (unprotected, or if protected by passing it explicitly) |
| tf panel local | personal (thru ssh agent, password can be passed explicitly) | personal (unprotected, or if protected by passing it explicitly) |
| tf panel deployed | machine key (thru ssh agent) | machine key |
| tf infra | n/a | (protected) personal key (with password propagated, somehow) |
## outcomes
added sub-tasks to:
- #272
- #76
- #274