App platform: Node connection to managed Redis fails

I’m trying to set up an example app with a Node.js Express server, a managed DO Redis db, and a Node.js worker.

I’m using the server.js and worker.js code from Heroku’s “node-workers-example”. I’m deploying by pushing containers to a DO Container Registry.

I got this app working locally with docker-compose, using the docker hub’s official redis image as the db, but I can’t get it to connect to my managed DO redis db.

(The code linked above doesn’t catch errors, but if I catch them, I see this):

Error: read ECONNRESET

MaxRetriesPerRequestError: Reached the max retries per request limit (which is 20). Refer to "maxRetriesPerRequest" option for details.

The app itself appears to just hang and timeout when I post to the /job endpoint and try to make the first connection do the DB.

Things I’ve checked:

• I attached the DB to my components in App Platform: it automatically added the env var DATABASE_URL, which I renamed to REDIS_URL to work with this code.
• The managed redis db is accepting connections from all sources. In fact, I wouldn’t know how to restrict it to the app platform even if I wanted to!
• The node package having this problem is bull, which uses ioredis under the hood to connect. I thought it might be a problem with TLS, but I was able to connect locally using ioredis with the same connection string (DATABASE_URL, which is rediss://default:<password, etc.>

I don’t know if the problem is specific to Node Bull here, but I don’t know how to begin debugging it beyond just logging as much as I can to the JS console.