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Fixes #7863. Connect command is `sudo snap connect certbot-dns-dnsimple:certbot-metadata certbot:certbot-metadata` Logs are `cat /var/snap/certbot-dns-dnsimple/current/debuglog` Echos in hook are only printed to terminal when it exits 0; otherwise, check logs in `debuglog` mentioned above. Manual tests include all iterations of connected, unconnected, installed for the first, second time, etc, with passing and failing version checks. * Make dnsimple not update if certbot is too old * create an interface to read cb version * add missing newline * fix syntax * trying to figure out the consumer syntax * trying to figure out the consumer syntax, again * only check post first install * valid setting name * test for first install differently * snapctl doesn't error if it fails I guess * time to do some print debugging * continue playing with syntax * once again, fooled by bash int vs string comparisons! * debugging * if we use post and pre together we can do this * is this how content interface syntax works * it's a directory? * more debug * what's that error message again? * try other syntax * if it's not documented just guess at syntax * actually, I think this is the syntax * oops didn't set for new hook * test passing information along connection * interface attributes can only be set during the execution of prepare hooks * just do it with main connection * undo last few test changes * Add some printing to make sure we understand what's going on * create empty directory to bind to * put mkdir in the correct part * let's inspect the environment * it can't run bash directly. * perhaps only directories can be shared via the contente interface * update name of folder * echo to debug log to understand what's going on exactly. we have file access though! * update grep for new file * more printing * echo to the debug log * ok NOW all print statements are going to the log * why does echo need two >s * remove unnecessary extra check, just check if the init file is available * check if certbot version will be available post-refresh after all * pre-refresh hook is not necessary to get certbot version * update mkdir so we don't have to clean each time * try comparing version numbers in python * it's python3 * we need different prints for if we succeed or if we fail. * improve bash syntax * remove some debugging code * Remove debug script * remove spaces for clarity * consolidate parts and remove more test code * s/certbot-version/certbot-metadata/g * use sys.exit instead of exit * find and save certbot version on the certbot side * change presence test to new file * switch to using packaging.version.parse instead of LooseVersion * switch to requiring certbot version >= plugin version * add plugin snap changes to generate script * Add comment to generation file saying not to edit generated files manually * Create post-refresh hook for all plugins with script * generate files using new script * update snapcraft.yaml files for plugins * bin/sh comes first * Add packaging to install_requires * Check that refresh is allowed in integration test * switch plug and slot names in integration test * Update tools/generate_dnsplugins_postrefreshhook.sh Co-authored-by: Brad Warren <bmw@users.noreply.github.com> * small bash fixes * Update snap readme with new instructions * Run tools/generate_dnsplugins_postrefreshhook.sh * Update tools/snap/generate_dnsplugins_postrefreshhook.sh Co-authored-by: Brad Warren <bmw@users.noreply.github.com> Co-authored-by: Brad Warren <bmw@users.noreply.github.com>
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Certbot Plugin Snaps
This is a proof of concept of how a Certbot snap might support plugin snaps that add functionality to Certbot using its existing plugin API.
Architecture
This is a description of how Certbot plugin functionality is exposed via snaps. For information on Certbot's plugin architecture itself, see the Certbot documentation on plugins.
The Certbot snap itself is a classic snap. Plugin snaps are regular confined snaps, but normally do not provide any "apps" themselves. Plugin snaps export loadable Python modules to the Certbot snap via a snap content interface.
Certbot itself accepts a CERTBOT_PLUGIN_PATH environment variable. This
support is currently patched but this is intended to be upstreamed. The
variable, if set, should contain a :-separated list of paths to add to
Certbot's plugin search path.
The Certbot snap runs Certbot via a wrapper which examines its list of
connected interfaces, sets CERTBOT_PLUGIN_PATH accordingly, and then execs
Certbot itself.
Use (Production)
Note: this production use example assumes that these snaps are available in stable channels in the Snap Store, which they aren't yet. See below for development instructions.
To use a Certbot plugin snap, install both the plugin snap and the Certbot snap
as usual. Plugin snaps are confined as normal; the Certbot snap is a classic
snap and thus needs --classic during installation. For example:
snap install --classic certbot
snap set certbot trust-plugin-with-root=ok
snap install certbot-dns-dnsimple
Then connect the plugin snap to the main certbot snap as follows. Note that this connection allows the plugin snap code to run inside the certbot process, which has access to your host system. Only perform this step if you trust the plugin author to have "root" on your system.
sudo snap connect certbot:plugin certbot-dns-dnsimple
Now certbot will automatically load and use the plugin when it is run. To check
that this has worked, certbot plugins should list the plugin.
You can now operate the plugin as normal.
Use (Testing and Development)
To try this out, you'll need to build the snaps (a patched Certbot snap and a plugin snap) manually.
Initial VM Set Up
These steps need to be done once to set up your VM and do not need to be run again to rebuild the snap.
- Start with a Focal VM. You need a full virtual machine using something like DigitalOcean, EC2, or VirtualBox. Docker won't work. Another version of Ubuntu can probably be used, but Focal was used when writing these instructions.
- Set up a user other than root with sudo privileges for use with snapcraft and run all of the following commands with it. A command to do this for a user named certbot looks like
adduser certbot && usermod -aG sudo certbot && su - certbot. - Install git and python with
sudo apt update && sudo apt install -y git python. - Set up lxd for use with snapcraft by running
sudo snap install lxd && sudo /snap/bin/lxd.migrate -yes && sudo /snap/bin/lxd waitready && sudo /snap/bin/lxd init --auto(errors here are ok; it may already have been installed on your system). - Add your current user to the lxd group and update your shell to have the new assignment by running
sudo usermod -a -G lxd ${USER} && newgrp lxd. - Install snapcraft with
sudo snap install --classic snapcraft. cd ~(or any other directory where you want our source files to be)- Run
git clone git://github.com/certbot/certbot cd certbot
Build the Snaps
These are the steps to build and install the snaps. If you have run these steps before, you may want to run the commands in the section below to clean things up before building the snap again.
- Run
snapcraft --use-lxd. - Install the generated snap with
sudo snap install --dangerous --classic certbot_*_amd64.snap. You can transfer the snap to a different machine to run it there instead if you prefer. - Run
tools/merge_requirements.py tools/dev_constraints.txt <(tools/strip_hashes.py letsencrypt-auto-source/pieces/dependency-requirements.txt) > certbot-dns-dnsimple/snap-constraints.txt(this is a workaround for https://github.com/certbot/certbot/issues/8100). cd certbot-dns-dnsimplesnapcraft --use-lxd- Run
sudo snap set certbot trust-plugin-with-root=ok. - Install the generated snap with
sudo snap install --dangerous certbot-dns-dnsimple_*_amd64.snap. Again, you can transfer the snap to a different machine to run it there instead if you prefer. - Connect the plugin with
sudo snap connect certbot:plugin certbot-dns-dnsimple. - Connect the plugin metadata with
sudo snap connect certbot-dns-dnsimple:certbot-metadata certbot:certbot-metadata. Install the plugin again to test refresh; logs are at/var/snap/certbot-dns-dnsimple/current/debuglog. - Now you can run Certbot as normal. For example,
certbot pluginsshould display the DNSimple plugin as installed.
Reset the Environment
The instructions below clean up the build environment so it can reliably be used again.
cd ~/certbot(or to an alternate path where you put our source files)snapcraft clean --use-lxdrm certbot_*_amd64.snapcd certbot-dns-dnsimplerm certbot-dns-dnsimple_*_amd64.snapsnapcraft clean --use-lxdcd ..
Publishing Permissions
There are security implications to permitting anyone to publish, without review, a plugin into the Snap Store which will then run in Certbot's classic snap context, with full access to the host system.
At a minimum, it is clear that this should happen only with the user's explicit opt-in action.
As implemented, Certbot will only load plugins connected via the snap interface mechanism, so permission is effectively delegated to what interface connections the snap infrastucture will permit.
We have approval from the snap team to use this design as long as we make it explicit what a user is agreeing to when they connect a plugin to the Certbot snap. That work was completed in https://github.com/certbot/certbot/issues/8013.
Outstanding issues
Outstanding items relating to plugin support in Certbot snaps are tracked on GitHub.