cap channels to 500 subscribers

value

• absent a signald replacement, channels past a certain size experience crippling message lag, and degrade system-wide behavior by causing health-check failures that trigger auto-restarts
• until we replace signald to provide better high-throughput availability, we would like to prevent channels from getting to the size where they degrade performance in this way
• SO: let's cap all new channels to 500 members, and existing channels to their current size (providing a per-channel threshold that can be raised upon special request via BOOST IT
• this will allow users of channels both big and small to have reasonable message lag and availability pending a deeper technical fix with signalc

behavior

JOIN flow

GIVEN a new channel #foo with 500 subscribers

• WHEN a rando sends HELLO
• THEN the rando will not be added to the channel and will recieve a message that says Sorry, this channel has reached its limit of 500 subscribers.

GIVEN an existing channel with 600 subscribers

• WHEN a rando sends HELLO
• THEN the rando will not be added and will receive the same message as above

GIVEN a new channel with 499 subscribers

• WHEN a rando sends HELLO
• THEN the rando will be added to the channel and receive a welcome message

INVITE flow

GIVEN an new channel #foo with 500 subscribers

• WHEN an admin or subscriber sends an invite to one person: INVITE <some rando's number>
• THEN the rando will not be invite to the channel
• AND THEN the inviting admin/subscriber will recieve a message that says Trying to invite 1 new subscriber? Sorry, this channel has reached its limit of 500 subscribers.

GIVEN an new channel #foo with 499 subscribers

• WHEN an admin or subscriber sends an invite to one person: INVITE <some rando number,>
• THEN a pending invite record will be creatd for therando
• AND THEN the inviter and invitee will receive the standard invite notifications

GIVEN an new channel #foo with 499 subscribers

• WHEN an admin or subscriber sends an invite to many people: INVITE <some rando number, some other rando number>
• THEN neither rando
• AND THEN the inviting admin/subscriber will recieve a message that says Trying to invite 2 new subscribers? Sorry, this channel has reached its limit of 500 subscribers.

GIVEN an existing channel with 600 subscribers

• same as above

ACCEPT flow

GIVEN an new channel #foo with 500 subscribers

• AND an invite that was issued to a rando before the channel reached 500 subscribers
• WHEN the rando tries to accept the invite by sending ACCEPT
• THEN the rando will not be invited to the channel
• AND THEN the rando will recieve a message that says Sorry, this channel has reached its limit of 500 subscribers.

GIVEN an new channel #foo with 499 subscribers

• AND an invite that was issued to a rando before the channel reached 500 subscribers
• WHEN the rando tries to accept the invite by sending ACCEPT
• THE rando is added to the channel and receives the standard welcome message

GIVEN an existing channel with 600 subscribers

• same as above

Admin exemption

GIVEN an new channel #foo with 500 subscribers

• WHEN an admin tries to add a new admin with ADD <some number>
• THEN the new admin is added as normal

maintainer overrides

GIVEN a new channel with 500 subscribers

• AND GIVEN a maintainer has used psql to set the channel's memberLimit to 600
• WHEN a rando sends HELLO
• THEN the rando will be added to the channel and receive a welcome message

user-facing docs

WHEN a user goes to signalboost.info/how-to

• THEN, they will see the following useful text in the Getting Started section:

4.  Send announcements to (up to 500) subscribers
Now, any anyone who sends "HELLO" to your channel number will get announcements you send out!

You can publish your channel phone number on Instagram or keep it to a close circle. Importantly, after your channel hits 500 subscribers new members will be prevented from subscribing until existing subscribers leave. Your channel will also take longer (up to 10mins) to send out broadcasts the larger it grows.

If you are in an urgent situation and would like to request a larger channel you can do so via 947-BOOSTIT (+1-947-800-5717). However, large channels put stress on our servers and team. 

We are working hard to make Signalboost support channels bigger than 500, but that work requires time and resources. You can help us get there by [donating!](/donate)

implementation

• add a subscriberLimit field to the channels table that defaults to 500
• run a migration that sets the memberLimit for all existing channels to either 500 or the current membership count (whichever is larger)
• add a docs guide for how to change the memberLimitField
• conditional subscriber count checks in maybeAddSubscriber and maybeIssueInvite

out of scope

• it might be nice to have a boost command to raise member limits on an ad-hoc basis without shutting down the app to use psql. we defer that work to a later card (#373 )