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Redis

{
  "uri": "redis://redis:6379",
  "username": null,
  "password": null,
  "mode": "pubsub",
  "default_channel": null,
  "streams": {
    "default_stream": null,
    "max_length": null,
    "exact_trimming": false,
    "data_field": "data",
    "claim_min_idle_ms": 60000
  },
  "tls": { "enabled": false, "client_certs": [], "trusted_certs": [], "trust_all": false, "hostname_verification": true, "start_tls": false },
  "io_thread_pool_size": null,
  "computation_thread_pool_size": null
}

uri is required: redis://, or rediss:// for TLS (which tls.enabled turns on too). The username and password are those of an ACL user (the password alone for the default user).

mode is pubsub or streams.

Pub/sub​

Channels: what is published reaches the subscribers there are, and no one else. A publish says how many subscribers got the message. Names with glob characters (*, ?, [) are patterns. Pub/sub has no acks, no groups and no replay; a subscriber too slow loses the oldest messages.

Streams​

An append-only log, with consumer groups and acks.

  • Publishing: XADD, the attributes of the event in ce_ fields next to the data_field. max_length trims the stream on each publish, to about that many entries (MAXLEN ~), exactly with exact_trimming (0 or null: no limit). The result gives the id of the entry.
  • Without a group: XREAD from now on (the last entry when subscribing: nothing slips between two reads), from the beginning (from=earliest), a date (from_timestamp) or an entry id (from_id, included). Every subscriber gets every entry. at-least-once needs a group.
  • With a group: XREADGROUP. The group is created where from says if it does not exist, and keeps its own position otherwise. An entry read by a member is its own until acked: as it leaves the subscription (at-most-once) or once handed over (at-least-once). What a member read and left unacked for claim_min_idle_ms (it went away, it was cut) is claimed by another member (XAUTOCLAIM) and delivered again, with redisredelivered.
  • Each subscription of a group is a consumer of its own, removed from the group when it goes away with nothing pending. consumer=<name> names it instead: a named consumer coming back gets what it had pending first (one subscription per name).
  • prefetch (100): what a read asks for. A smaller prefetch shares the entries more evenly between slow members.
  • An entry added by another producer without a data_field is read with all its fields as a JSON object (XADD orders * user 42 gives {"user": "42"}).
  • Server-sent events resume right after the last entry a client got, stream by stream.
  • Lag: what XINFO GROUPS says of a group (see Observability).