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25 lines
1.9 KiB
Markdown
25 lines
1.9 KiB
Markdown
# Publish Subscribe
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NATS implements a publish subscribe message distribution model as a one-to-many communication. A publisher sends a message on a subject and any active subscriber listening on that subject receives the message. Subscribers can also register interest in wildcard subjects that work a bit like a regular expression (but only a bit). NATS and NATS Streaming combine to offer two qualities of service:
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- **At Most Once Delivery (NATS w/TCP reliability)** - In the basic NATS platform, if a subscriber is not listening on the subject (no subject match), or is not active when the message is sent, the message is not received. NATS is a fire-and-forget messaging system. If you need higher levels of service, you can either use NATS Streaming, or build the additional reliability into your client(s) yourself.
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- **At Least Once Delivery (NATS Streaming)** - Some applications require higher levels of service and more stringent delivery guarantees but at the potential cost of lower message throughput and higher end-to-end delivery latency. These applications rely on the underlying messaging transport to ensure that messages are delivered to subscribers irrespective of network outages or whether or not a subscriber is offline at a particular point in time.
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<div class="graphviz"><code data-viz="dot">
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digraph nats_pub_sub {
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rankdir=LR
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publisher [shape=box, style="rounded", label="Publisher"];
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subject [shape=circle, label="Subject"];
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sub1 [shape=box, style="rounded", label="Subscriber"];
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sub2 [shape=box, style="rounded", label="Subscriber"];
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sub3 [shape=box, style="rounded", label="Subscriber"];
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publisher -> subject [label="msg1"];
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subject -> sub1 [label="msg1"];
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subject -> sub2 [label="msg1"];
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subject -> sub3 [label="msg1"];
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}
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</code></div>
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Try NATS publish subscribe on your own, using a live server by walking through the [pub-sub tutorial](../tutorials/pubsub.md). |