Consumers

Natscope supports both pull and push consumers, durable and ephemeral.

All consumers at once

Consumers in the sidebar lists every consumer on the connection, across all streams. Each row shows what the consumer has not delivered yet (Pending), what waits for an ack out of the most it allows (Waiting for ack), how many unacknowledged messages went out more than once (Redelivered) and when it last delivered. Stuck consumers come first, then the ones with the most pending messages.

The Status column names the problem in plain words. Hover a badge for the details.

Badge	Means
Ack limit reached	As many messages wait for an ack as max ack pending allows, and no ack came in lately. The server delivers nothing new until clients ack or the ack wait runs out.
At its ack limit	The same limit, but clients are still acking: the consumer is busy, not stuck.
No subscriber	A push consumer has messages to deliver and nobody subscribes to its deliver subject.
Nobody pulling	A pull consumer has messages to deliver, no pull request waits, and no client pulled in the last minute.
Redelivering	Messages still wait for an ack, and some were delivered again: a client rejected them or missed the ack wait.
May lose messages	The stream is at least 90% full and drops its oldest messages, and the next message for this consumer is among the oldest tenth.
Losing messages	The same, and the stream already dropped messages this consumer had not reached.
Paused	Delivery is paused until the time shown.

Natscope raises May lose messages and Losing messages only for a consumer that sees the whole stream: one without a filter, or whose filter takes every subject of the stream. For a filtered consumer the server does not say which of the dropped messages were on its subjects.

A consumer with nothing wrong is Catching up while it has work left, and Caught up when it has none.

The page reads the consumers every 5 seconds; turn Auto-refresh off to freeze the numbers. Problems only hides the healthy consumers, the filter matches consumer names, streams and filter subjects, and the download button exports the list as CSV or JSON in the order shown. Stuck consumers come first; click a column header to sort by it instead, and click it again to reverse the order. Click a row to open the consumer on its stream; Cmd/Ctrl-click or middle-click opens it in a new tab.

The server keeps the time of the last delivery in memory only, so after a server restart Last delivery says unknown until the consumer delivers again. Natscope's own short-lived consumers, which it creates to read streams, are left out.

If the NATS user may not list the consumers of some streams, the page says which streams are missing and which permission the server refused. If it may not list streams at all, the page names that permission instead.

Where a consumer is

The view of a consumer starts with What holds it back when one of the problems above applies. Where it is shows:

• Oldest waiting for ack: the first delivered message no client acknowledged. The consumer cannot move its ack floor past it. With a delivery limit, it may instead be a message that ran out of delivery attempts: the server reports no floor past such a message until every later one is acknowledged.
• Next to deliver: the next new message for the consumer. Redeliveries of unacknowledged messages go out before it.
• How far the consumer delivered, and up to where every message is done in order.
• Which messages left the stream before the consumer reached them, when that happened and the consumer sees the whole stream.

Open shows the message on the stream's Messages tab. Natscope reads these messages straight from the stream, so looking at them does not deliver or acknowledge anything.

What happened to a message

The details of a stream message have a Consumers line: how many consumers are done with it, got it and still owe an ack, or have not received it yet. Expand it to see each consumer:

• Done: acknowledged, terminated by a client, or out of delivery attempts; the server does not report which. Once no message waits for an ack, every delivered message counts as done.
• Waiting for ack: delivered, not acknowledged yet. With explicit acks a client may have acknowledged it out of order, which the server does not report per message.
• Not delivered yet: still in line for this consumer
• Skipped: the consumer starts after this message, so it never gets it
• Delivered: delivered to a consumer that does not use acks
• … or skipped: the consumer started from the last message, or the last message per subject, so a message from before it was created may have been skipped instead

Consumers whose filter leaves the subject out are counted separately.

Create a consumer

1. Open a stream, go to the Consumers tab.
2. Click Create New Consumer.
3. Fill in the config and save.

The form covers the JetStream consumer surface:

• Delivery policy: all, last, new, by start sequence, by start time
• Ack policy: none, all, explicit
• Filter subjects: one or several
• Backoff: an array of redelivery delays
• Max deliver and max ack pending
• Flow control for push consumers
• Deliver subject and deliver group for push consumers
• Replicas

Edit a consumer

Select a consumer, change the fields, and save. Natscope shows Confirm Consumer Configuration Changes with a field-level diff before it sends anything to the server.

Pause and resume

Pause stops delivery until a chosen time. Paused consumers carry a paused-until badge in the list. Resume lifts it early. Needs NATS 2.11+.

Reset

Reset clears the delivery state so unacknowledged messages are delivered again, without deleting the consumer. Leave the sequence empty to keep the ack floor, or enter a stream sequence to replay from it. Replaying from a sequence works for consumers that deliver all messages or start at a sequence or time. Needs NATS 2.14+.

Priority groups

Pull consumers can split work between clients through priority groups (NATS 2.11+). Set them in the Priority Groups section of the form:

• Pinned client sends every message to one client until it stays idle longer than the pinned TTL
• Overflow serves a client only when the others fall behind
• Prioritized prefers clients with a lower priority number (NATS 2.12+)

The consumer view shows which client each group is pinned to. Unpin releases it, so the next pull request gets pinned instead.

Delete

Deleting a consumer asks for confirmation by default. Turn that prompt off under Settings → Preferences → Behavior.

Copy as nats CLI

Copy as nats CLI turns the selected consumer config into a nats consumer add command you can paste into a terminal or commit to a repo.