Migrated from HedgeDoc. Notes taken in 2022 that still have relevancy today (Oct 2026).
Lemmy federation to Mastodon breaks down
A possible example of Post-facto interop, newly encountered issues with federation between Mastodon and Lemmy, which was working relatively fine when Lemmy release federation support.
- In Friendica you can create new Lemmy posts, but Mastodon until now never supported that.
- When Lemmy launched federation support, on Mastodon you could properly interact with Lemmy posts of followed Communities.
- Federation functionality to Mastodon is now broken due to (likely) changes on Mastodon side. There seem to be multiple issues.
- One bug mentioned in reply to the discussion sees Mastodon boosting all Lemmy comments, which is spamming timelines.
- @userthree creates a Lemmy issue: Federating with Mastodon - Don’t boost comments
- An analysis of core devs of Lemmy (Nutomic) and Mastodon (ClearlyClaire) ensues.
- Lemmy announces group actions by wrapping in
Announcee.g.Announce{Create{Note}}. - This was unsupported on Mastodon so Lemmy created a fallback to send
Announce{Note}. - Earlier issue of ‘too much noise’ led to Dont announce comments, edited posts to Pleroma/Mastodon followers
- So Lemmy changed it to
Announce{Page}andAnnounce{Create{Page}}. On Mastodon this breaks Post comment threads. - It was observed that both Lemmy and Mastodon have (their own different) shortcomings to reply-handling.
- Boosted comments bug was found to be caused by new functionality added in Mastodon 3.5 and an unintended side-effect.
- Mastodon PR causing bug is Add support for fetching Create and Announce activities by URI in prep for Post Editing, Group support.
- Nutomic now closes the issue, as not Lemmy-related.
- @userthree now creates a similar issue in the Mastodon issue tracker, pointing to the closed Lemmy issue analysis.
- @Nightpool of Mastodon reacts that ‘this makes no sense’, everything works as it should, closes the issue.
- This comment came affter Nutomic already closed the Lemmy issue, so they likely are not aware of it (I added a heads-up).
- In the fediverse discussion @Liwott mentions that closing both issues like that is ‘a bit harsh’, and there’s benefit to fixing on both sides.
- Note: The benefit is clearly greater on Lemmy’s side, the smaller party, who will miss out on a lot of Mastodon-based interaction.
Now, it is not 100% clear if this is post-facto interop, where Mastodon on their own as dominant part introduces new features (Post Editing) that breaks other application’s functionality unless they catch up. This may also relate to the ongoing ad-hoc interop where everyone adds their own Groups functionality. See Ad-hoc interoperability: Groups standardization.
Observations
- There are no standards to this. Every app is iterating on their own, creating possible breakages with other apps.
- There is no visibility to what is happening. Knowledge is spread in multiple issue trackers, many issues, numerous cross-references.
- Only involved expert devs have a clear picture what is going on, at the moment of analysis. They’ll likely forget much of that context.
- Numerous people report/discuss the observed bugs, and eat time of the devs having to respond (see e.g. this Lemmy post).
- Github helps by creating cross-references between issues, but for apps on different code forges this benefit doesn’t exist.
Assumptions
- Dominant, most active and fast-moving project will dictate the protocol implementation and changes, other projects must follow.
- Breakages like this will become the norm, and fixing them a ‘whack-a-mole’ time-absorbing and frustrating process.
- Likely many apps won’t spend effort in broad federation, federate just with themself or their domain (fractured interop islands).
- Likely all the breakages will turn off fedizens, who’ll either stick to dominant/popular apps, or leave the Fediverse altogether.
- → Post-facto interoperability pays off, and leading positions of already dominant apps will be further cemented.