I used your dockerfile to build the latest rocket.chat and also started Mongo with your compose recommendations.
/app/bundle/programs/server/node_modules/fibers/future.js:313
throw(ex);
^
MongoError: not master and slaveOk=false
at Connection.<anonymous> (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/core/connection/pool.js:451:61)
at Connection.emit (events.js:311:20)
at processMessage (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/core/connection/connection.js:452:10)
at Socket.<anonymous> (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/core/connection/connection.js:621:15)
at Socket.emit (events.js:311:20)
at addChunk (_stream_readable.js:294:12)
at readableAddChunk (_stream_readable.js:275:11)
at Socket.Readable.push (_stream_readable.js:209:10)
at TCP.onStreamRead (internal/stream_base_commons.js:186:23) {
operationTime: Timestamp { _bsontype: 'Timestamp', low_: 1, high_: 1605988825 },
ok: 0,
code: 13435,
codeName: 'NotMasterNoSlaveOk',
'$clusterTime': {
clusterTime: Timestamp { _bsontype: 'Timestamp', low_: 1, high_: 1605988825 },
signature: { hash: [Binary], keyId: 0 }
},
name: 'MongoError'
}