# GnatStreaming
A [NATS Streaming](https://nats.io/documentation/streaming/nats-streaming-intro/) client for Elixir.
## Installation
:warning: This is an alpha-stage piece of code.
I have tested it end-to-end, but not run it in production.
The API is liable to change as I experiment with better ways of managing the complexity of a streaming and acknowledging messages.
To use this, just add it to your mix deps.
```elixir
def deps do
[
{:gnat_streaming, "~> 0.0.1"}
]
end
```
## Architecture
In the long run, I hope to encompass all the common use-cases of NATS streaming into a simple API in the `Gnat.Streaming` module.
Since I don't yet know what the common use-cases are, and what will be required in terms of structure, I am mostly focused on the level of abstraction below that.
Currently, I'm thinking we will end up with a process architecture like:
We will leave the details of managing TCP/TLS connections and the low-level protocol to the [nats.ex library](https://github.com/nats-io/nats.ex).
In order to do any NATS streaming activities, we start up a `Streaming.Client` process which is given the name of a `Gnat` (provided by nats.ex).
The client process is a state machine that finds and monitors the `Gnat` process and registers itself as a nats streaming client.
We can also start `Streaming.Subscription` processes that find and monitor the `Streaming.Client` process (as well as monitoring the `Gnat` process).
These processes wait for the client to be registered and then use metadata about the client to open a subscription.
As messages start to come in for the given topic, they are decoded and we run the `consuming_function` specified when starting that subscription in a [Task](https://hexdocs.pm/elixir/1.9.1/Task.html).
Your `consuming_function` should accept a single argument (a `Streaming.Message` struct), and should call `Message.ack/1` once you have ensured that it has been handled.
> Since each message is handled in its own process, this can quickly saturate all cores on a machine.
> Please use the `max_in_flight` option when opening your subscription to limit how many message you want to run in parallel.
Subscriptions monitor the `Streaming.Client` and the `Gnat` connection to automatically re-subscribe if the connection goes down temporarily.
## Benchmarking
Most of the performance concerns I have for this library are around steady-state throughput.
So I've opted for a benchmarking strategy where data is collected into an external service.
In order to make this all work I start things up like this:
```
docker run -it --rm -p 3003:3003 -p 3004:8888 -p 8086:8086 -p 8125:8125/udp samuelebistoletti/docker-statsd-influxdb-grafana:latest
nats-streaming-server -m 8222 -mm 10000000
```
Once both of those are up and running you can run a benchmark like:
```
mix run bench/pulish.exs
```
Then go to `http://localhost:3003/`, login with credentials `root`/`root` and import a dashboard like this:
<details>
<summary>Grafana Dashboard</summary>
```json
{
"annotations": {
"list": [
{
"builtIn": 1,
"datasource": "-- Grafana --",
"enable": true,
"hide": true,
"iconColor": "rgba(0, 211, 255, 1)",
"name": "Annotations & Alerts",
"type": "dashboard"
}
]
},
"editable": true,
"gnetId": null,
"graphTooltip": 0,
"id": 2,
"links": [],
"panels": [
{
"aliasColors": {},
"bars": false,
"dashLength": 10,
"dashes": false,
"datasource": "InfluxDB",
"fill": 1,
"gridPos": {
"h": 8,
"w": 24,
"x": 0,
"y": 0
},
"id": 4,
"legend": {
"avg": false,
"current": false,
"max": false,
"min": false,
"show": true,
"total": false,
"values": false
},
"lines": true,
"linewidth": 1,
"links": [],
"nullPointMode": "null",
"paceLength": 10,
"percentage": false,
"pointradius": 2,
"points": false,
"renderer": "flot",
"seriesOverrides": [],
"stack": false,
"steppedLine": false,
"targets": [
{
"alias": "Received/sec",
"groupBy": [
{
"params": [
"1s"
],
"type": "time"
},
{
"params": [
"null"
],
"type": "fill"
}
],
"measurement": "recvd",
"orderByTime": "ASC",
"policy": "default",
"refId": "A",
"resultFormat": "time_series",
"select": [
[
{
"params": [
"value"
],
"type": "field"
},
{
"params": [],
"type": "sum"
}
]
],
"tags": []
}
],
"thresholds": [],
"timeFrom": null,
"timeRegions": [],
"timeShift": null,
"title": "Received per Sec",
"tooltip": {
"shared": true,
"sort": 0,
"value_type": "individual"
},
"type": "graph",
"xaxis": {
"buckets": null,
"mode": "time",
"name": null,
"show": true,
"values": []
},
"yaxes": [
{
"format": "short",
"label": null,
"logBase": 1,
"max": null,
"min": null,
"show": true
},
{
"format": "short",
"label": null,
"logBase": 1,
"max": null,
"min": null,
"show": true
}
],
"yaxis": {
"align": false,
"alignLevel": null
}
},
{
"aliasColors": {},
"bars": false,
"dashLength": 10,
"dashes": false,
"datasource": "InfluxDB",
"fill": 1,
"gridPos": {
"h": 8,
"w": 24,
"x": 0,
"y": 8
},
"id": 6,
"legend": {
"avg": false,
"current": false,
"max": false,
"min": false,
"show": true,
"total": false,
"values": false
},
"lines": true,
"linewidth": 1,
"links": [],
"nullPointMode": "null",
"paceLength": 10,
"percentage": false,
"pointradius": 2,
"points": false,
"renderer": "flot",
"seriesOverrides": [],
"stack": false,
"steppedLine": false,
"targets": [
{
"alias": "Ack/sec",
"groupBy": [
{
"params": [
"1s"
],
"type": "time"
},
{
"params": [
"null"
],
"type": "fill"
}
],
"measurement": "ackd",
"orderByTime": "ASC",
"policy": "default",
"refId": "A",
"resultFormat": "time_series",
"select": [
[
{
"params": [
"value"
],
"type": "field"
},
{
"params": [],
"type": "sum"
}
]
],
"tags": []
}
],
"thresholds": [],
"timeFrom": null,
"timeRegions": [],
"timeShift": null,
"title": "Acks per Second",
"tooltip": {
"shared": true,
"sort": 0,
"value_type": "individual"
},
"type": "graph",
"xaxis": {
"buckets": null,
"mode": "time",
"name": null,
"show": true,
"values": []
},
"yaxes": [
{
"format": "short",
"label": null,
"logBase": 1,
"max": null,
"min": null,
"show": true
},
{
"format": "short",
"label": null,
"logBase": 1,
"max": null,
"min": null,
"show": true
}
],
"yaxis": {
"align": false,
"alignLevel": null
}
},
{
"aliasColors": {},
"bars": false,
"dashLength": 10,
"dashes": false,
"datasource": "InfluxDB",
"fill": 1,
"gridPos": {
"h": 9,
"w": 24,
"x": 0,
"y": 16
},
"id": 2,
"legend": {
"avg": false,
"current": false,
"max": false,
"min": false,
"show": true,
"total": false,
"values": false
},
"lines": true,
"linewidth": 1,
"links": [],
"nullPointMode": "null",
"paceLength": 10,
"percentage": false,
"pointradius": 2,
"points": false,
"renderer": "flot",
"seriesOverrides": [],
"stack": false,
"steppedLine": false,
"targets": [
{
"alias": "pub/sec",
"groupBy": [
{
"params": [
"1s"
],
"type": "time"
},
{
"params": [
"null"
],
"type": "fill"
}
],
"measurement": "pubd",
"orderByTime": "ASC",
"policy": "default",
"refId": "A",
"resultFormat": "time_series",
"select": [
[
{
"params": [
"value"
],
"type": "field"
},
{
"params": [],
"type": "sum"
}
]
],
"tags": []
}
],
"thresholds": [],
"timeFrom": null,
"timeRegions": [],
"timeShift": null,
"title": "Pubs per Second",
"tooltip": {
"shared": true,
"sort": 0,
"value_type": "individual"
},
"type": "graph",
"xaxis": {
"buckets": null,
"mode": "time",
"name": null,
"show": true,
"values": []
},
"yaxes": [
{
"format": "short",
"label": null,
"logBase": 1,
"max": null,
"min": null,
"show": true
},
{
"format": "short",
"label": null,
"logBase": 1,
"max": null,
"min": null,
"show": true
}
],
"yaxis": {
"align": false,
"alignLevel": null
}
}
],
"schemaVersion": 18,
"style": "dark",
"tags": [],
"templating": {
"list": []
},
"time": {
"from": "now-15m",
"to": "now"
},
"timepicker": {
"refresh_intervals": [
"5s",
"10s",
"30s",
"1m",
"5m",
"15m",
"30m",
"1h",
"2h",
"1d"
],
"time_options": [
"5m",
"15m",
"1h",
"6h",
"12h",
"24h",
"2d",
"7d",
"30d"
]
},
"timezone": "",
"title": "Gnat Streaming",
"uid": "D-RMocGWz",
"version": 4
}
```
</details>
