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Caddy-NATS

caddy-nats is a caddy module that allows the caddy server to interact with a NATS server. This extension supports multiple patterns: publish/subscribe, fan in/out, and request reply.

The purpose of this project is to better bridge HTTP based services with NATS in a pragmatic and straightforward way. If you've been wanting to use NATS, but have some use cases that still need to use HTTP, this may be a really good option for you.

Installation

To use caddy-nats, simply run the xcaddy build tool to create a caddy-nats compatible caddy server.

xcaddy build --with github.com/codegangsta/caddy-nats

Getting Started

Getting up and running with caddy-nats is pretty simple:

First install NATS and make sure the NATS server is running:

nats-server

Then create your Caddyfile:

{
  nats {
    reply hello GET https://localhost/hello
  }
}

localhost {
  route /hello {
    respond "Hello, world"
  }
}

After running your custom built caddy server with this Caddyfile, you can then run the nats cli tool to test it out:

nats req hello ""

Connecting to NATS

To connect to nats, simply use the nats global option in your Caddyfile:

{
  nats
}

This will connect to the currently selected nats context that the nats CLI uses. If there is no nats context available, it will connect to the default nats server URL.

You can view your nats context information via the nats cli:

nats context list

We recommend connecting to a specific context:

{
  nats <context>
}

Subscribing to a NATS subject

caddy-nats supports subscribing to NATS subjects in a few different flavors, depending on your needs.

Subscribe Placeholders

All subscribe based directives (subscribe, reply, queue_subscribe, queue_reply) support the following caddy placeholders in the method and url arguments:

  • {nats.path}: The subject of this message, with dots "." replaced with a slash "/" to make it easy to map to a URL.
  • {nats.path.*}: You can also select a segment of a path ex: {nats.path.0} or a subslice of a path: {nats.path.2:} or {nats.path.2:7} to have ultimate flexibility in what to forward onto the URL path.

subscribe

Syntax

subscribe <subject> <method> <url>

subscribe will subscribe to the specific NATS subject (wildcards are supported) and forward the NATS payload to the specified URL inside the caddy web server. This directive does not care about the HTTP response, and is generally fire and forget.

Example

Subscribe to an event stream in NATS and call an HTTP endpoint:

{
  nats {
    subscribe events.> POST https://localhost/nats_events/{nats.path.1:}
  }
}

reply

Syntax

reply <subject> <method> <url>

reply will subscribe to the specific NATS subject and forward the NATS payload to the specified URL inside the caddy web server. This directive will then respond back to the nats message with the response body of the HTTP request.

Example

Respond to the hello.world NATS subject with the response of the /hello/world endpoint.

{
  nats {
    reply hello.world GET https://localhost/hello/world
  }
}

queue_subscribe

Syntax

queue_subscribe <subject> <queue> <method> <url>

queue_subscribe operates the same way as subscribe, but subscribes under a NATS queue group

Example

Subscribe to a worker queue:

{
  nats {
    queue_subscribe jobs.* workers_queue POST https://localhost/{nats.path}
  }
}

queue_reply

Syntax

queue_reply <subject> <queue> <method> <url>

queue_reply operates the same way as reply, but subscribes under a NATS queue group

Example

Subscribe to a worker queue, and respond to the NATS message:

{
  nats {
    queue_reply jobs.* workers_queue POST https://localhost/{nats.path}
  }
}

Publishing to a NATS subject

caddy-nats also supports publishing to NATS subjects when an HTTP call is matched within caddy, this makes for some very powerful bidirectional patterns.

Publish Placeholders

All publish based directives (nats_publish, nats_request) support the following caddy placeholders in the subject argument:

  • {nats.subject}: The path of the http request, with slashes "/" replaced with dots "." to make it easy to map to a NATS subject.
  • {nats.subject.*}: You can also select a segment of a subject ex: {nats.subject.0} or a subslice of the subject: {nats.subject.2:} or {nats.subject.2:7} to have ultimate flexibility in what to forward onto the URL path.

Additionally, since publish based directives are caddy http handlers, you also get access to all caddy http placeholders.

nats_publish

Syntax

nats_publish [<matcher>] <subject> {
  timeout <timeout-ms>
}

nats_publish publishes the request body to the specified NATS subject. This http handler is not a terminal handler, which means it can be used as middleware (Think logging and events for specific http requests).

Example

Publish an event before responding to the http request:

localhost {
  route /hello {
    nats_publish events.hello
    respond "Hello, world"
  }
}

nats_request

Syntax

nats_request [<matcher>] <subject> {
  timeout <timeout-ms>
}

nats_request publishes the request body to the specified NATS subject, and writes the response of the NATS reply to the http response body.

Example

Publish an event before responding to the http request:

localhost {
  route /hello/* {
    nats_request hello_service.{nats.subject.1}
  }
}

What's Next?

While this is currently functional and useful as is, here are the things I'd like to add next:

  • Add more examples in the /examples directory
  • Add Validation for all caddy modules in this package
  • Add godoc comments
  • Support mapping nats headers and http headers for upstream and downstream
  • Customizable error handling
  • Jetstream support (for all that persistence babyyyy)
  • nats KV for storage