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World MoveIt Day Chat: Slack or Discord?

Quick vote - at our Working Group meeting yesterday we agreed on using Slack to organize our virtual World MoveIt Day event on Tuesday. I was about to setup it up, and still can, but wanted to ask:

Should we use Slack or Discord? This article argues open source projects shouldn’t.

Pro: almost everyone seems to use Slack for work
Con: the free version doesn’t really save message history (limit is 10k)

Discord doesn’t have the limitation, and is already popular with gamers. I’m fine going either way, just wanted to gut-check this. @smac how’s Slack going for Navigation?

Check back before Tuesday for an invite link to one or the other.


Prenote: I hadn’t used discord before but I also forgot how much I absolutely hate to use Slack or Slack-like things professionally. To me, it is a complete productivity killer and the search features are the worst in any industry I’ve ever seen. For me as maintainer though, Slack is rather nice place for me to pop in and steer a conversation in the right direction, PM with developers needing special attention, and lead projects. If I were a company, I would avoid Slack and things like it like the plague, but as a community maintainer trying to build a community its great. Its not really a productivity killer in this context because by answering Slack and engaging in it, that is the work itself. I see why project managers love it, but at the cost of all of the engineering team being constantly distracted.


The 10k message limit isn’t a big deal to me, except for one reason (I’ll come back to that). Any real discussion should be happening on tickets or summaries of discussions had on these platforms should be on tickets later. This is also intuitive because people file tickets in the GitHub issue tracker, you respond there, you might sidebar in Slack to design a solution, but in the end you pop back out on the ticket with a summary and PR to fix the issue or implement the feature.

Because Slack/Discord aren’t openly searchable (no Google results for a traceback or keyword) these services should never be relied on for an archive of an important discussion. In that respect, I don’t care about the 10k message limit because anything worth remembering is translated or occurring in tickets. How often do you read emails from 2 months ago? Almost never. Same concept applies here. The searchable tickets / conversations in GitHub to me are the prize goal, because that’s how I learned ROS and got a bunch of historical context about design discussions and questions raised when some of this work was first being introduced. That is one of the most powerful habits formed at Willow Garage that made ROS such a great tool. You could gain massive insight years after the fact from strangers far, far away (as long as you were willing to dig).

Now what is bad is that if I have some pinned posts, say, I spent hours to elaborate on some really technical concept and I want that to be findable in the future, the 10k limit may wipe them out. I can’t find documentation from Slack about it. The best I can find is this one off reddit comment that says its kept, but I’m wary of trusting that.

We’ve been using Slack for about a month and a half now and hit about 40% of that 10k limit. So its not as if that limit will be clearing the queue every week or two or you lose anything as part of some recent discussion. We also have over 200 members and a few really active channels. The 10k limit to me is fully satisfactory, I think you’d have to hit the 500 person mark before it would become too much of a problem.

We have so much momentum on Slack, so I can’t start over, but if I were I’d take a hard look at discord because of my uncertainty around pinned posts. This assumes that the concept of pinned posts exists in Discord as well. If it doesn’t then I’d go back to Slack.

But overall, I’ve been really happy with how things have worked out so far. I can’t really complain (unless pinned posts are deleted, then you’ll really hear my thoughts).

Postnote: Slack has some community programs that will give you Slack for free. Things are weird right now with COVID so their community program is focsed on COVID response companies, but if you apply, its auto-approved for a 3 month trial. Once that starts winding down for Navigation2, I’ll consider reaching out to Slack directly and getting it extended indefinitely since this is an open source project. Samsung loves ROS, but I don’t know that I can get Samsung to pay for 200 people * $6.67 a month for $16,000 a year for Slack. If I could inject $16,000 into ROS somewhere, this wouldn’t be that place. It would probably be the build farm or something.

Just want to pop in and give some love to Matrix and Riot
Riot is essentially an open source, end to end encrypted, and decentralized alternative of Discord built on the Matrix network. Take a look at it if you want open source!

Something really powerful with Matrix are bridges so that you can have Discord and Slack and Matrix users all talking in the same room/channel. See:


Pro: almost everyone seems to use Slack for work

Sorry Dave, but from my perspective that’s a trendy-robotics-company social filter bubble and no valid argument. I’d never even heard of Slack if it weren’t for you (seriously). :wink:

If you want to set it up for WMD the storage limit does not matter anyway and anyone relying on information not written down in github issues should put it there.

According to online documentation, discord’s video chat is limited to 9 participants and slack to 15.

I’m personally a friend of slack-alternatives (open source if possible), simply to avoid the monopoly.

But this is nothing permanent (at least not from my perspective), so the only important thing is that you set something up today and post it here :slight_smile:

Pro: almost everyone seems to use Slack for work

While the interface might be more familiar, people still have to create new Slack accounts. With Matrix/Riot this is not the case.
With Riot’s embedded video call service (Jitsi), the max participants are 75 but mileage varies depending on video on/off, etc.

Discord seems to be easiest to join for general public. Added PR:

I sorta understand the decision, but makes me very sad that a closed source option was chosen :cry:
hopefully one day ROS will be able to break out of closed source communication.

Nothing about that has to be permanent, I think this was just a matter of convenience and time constraints.

For completeness, I’ve heard good things about

@felixvd does not have an extension bridge support as Matrix. I believe it only has a Slack bridge.

For the record (since this still comes up on Google), we went with the Discord: