VyOS remote management library for Python
Posted 6 Sep, 2016 by Daniil Baturin
Someone on Facebook rightfully noted that lately there's been more work on the infrastructure than development. This is true, but that work on infrastructure was long overdue and we just had to do it some time. There is even more work on the infrastructure waiting to be done, though it's more directly related to development, like restructuring the package repos.
Anyway, it doesn't mean all development has stopped while we've been working on infrastructure. Today we released a Python library for managing VyOS routers remotely.
Before I get to the details, have a quick example of what using it is like:
vyos = vymgmt.Router('192.0.2.1', 'vyos', password='vyos', port=22)
vyos.set("protocols static route 203.0.113.0/25 next-hop 192.0.2.20")
vyos.delete("system options reboot-on-panic")
If you want to give it a try, you can install it from PyPI ("pip install vymgmt"), it's compatible with both Python 2.7 and Python 3. You can read the API reference at http://vymgmt.readthedocs.io/en/latest/ or get the source code at https://github.com/vyos/python-vyos-mgmt .
Now to the details. This is not a true remote API, the library connects to VyOS over SSH and sends commands as if it was a user session. Surprisingly, one of the tricky parts was to find an SSH/expect library that can cope with VyOS shell environment well, and is compatible with both 2.7 and 3. All credit for this goes to our contributor who goes by Hochikong, who tried a whole bunch of them, settled with pexpect and wrote a prototype.
How the library is better than using pexpect directly, if it's a rather thin wrapper for it? First, it's definitely more convenient to just call set() or delete() or commit() than to format command strings yourself and take care of the sending and receiving lines.
Second, common error conditions are detected (through simple regex matching) and raise appropriate exceptions such as ConfigError (for set/delete failures) or CommitError for commit errors. There's also a special ConfigLocked exception (a subclass of CommitError) that is raised when commit fails due to another commit in progress, so you can recover from it by sleep() and retry. This may seem uncommon, but people who use VRRP transition scripts and the like on VyOS already reported that they ran into it.
Third, the library is aware of the state machine of VyOS sessions, and will not let you accidentally do wrong things such as trying to enter set/delete commands before entering the conf mode. By default it also doesn't let you exit configure sessions if there are uncommited or unsaved changes, though you can override it. If a timeout occursm an exception will be raised too (while pexpect returns False in this case).
Right now it only supports set, delete, and commit, of all high level methods. This should be enough for the start, but if you want something else, there are generic methods for running op and conf mode commands (run_op_mode_command() and run_conf_mode_command() respectively). We are not sure what people want most, so what we implement depends on your requests ans suggestions (and pull requests of course!). Other things that are planned but that aren't there yet are SSH public key auth and top level words other than set and delete (rename, copy etc.). We are not sure if commit-confirm is really friendly to programmatic access, but if you have any ideas how to handle it, share with us.
On an unrelated note, syncer and his graphics designer friend made a design for VyOS t-shirts. If anyone buys that stuff, the funds will be used for the project needs. The base cost is around 20 eur, but you can get them with 15% discount by using VYOSMGTLIB promo code: https://teespring.com/stores/vyos?source=blog&pr=VYOSMGTLIB