api-express-exporter

api-express-exporter is a prometheus exporter that helps you track express api requests. Plug it in and start monitoring express api requests!

const app = express();

...

// Before all routes
app.use(require("api-express-exporter")()); // That's it!

// Apply your routes
app.get('hello', (req, res) => {
  res.json({ 'hello': 'world!'})
});

Difference between api-express-exporter and other prometheus-api-exporters

api-express-exporter has three goals:

1. Allow you to aggregate metrics by the actual pattern across nested routers.

request path	maps to path
/api/sub/2/more/3	/api/sub/:id/more/:id2
/api/sub/30/more/50/	/api/sub/:id/more/:id2
/api/error	/api/error
/api/users/1	/api/users/:userId
/api/users/100	/api/users/:userId
/api/users/badId	/api/users/:userId
/api/users/uuid	/api/users/:userId

api-express-exporter will not guess or replace your route params. It will map them to the original pattern.

It does this by extracting your actual routes with express-list-endpoints, and then create url-pattern for each route. When a request comes in, api-express-exporter will use the UrlPattern objects to retrieve the original route pattern.

This is essential for large applications, if you have tens of thousands of products in a database collection, you do not want separate time series for each product, you want to see them all show up under /api/products/:productId.

Losing the original path param names is also error-prone, some frameworks will map both /api/products/500 and /api/users/500 to /api/products/:id and /api/users/:id, making it hard to read at a glance. We want /api/users/:userId and /api/products/:productId

2. Zero configuration to start with. Use reasonable defaults.
3. Keep things simple. 100 lines total in one file. Easy to fork and update.

Installation

This is a Node.js module available through the npm registry.

Before installing, download and install Node.js. Node.js 0.10 or higher is required.

Installation is done using the npm install command:

$ npm install api-express-exporter

This package depends on express, prom-client, express-list-endpoints, express-prom-bundle, and url-pattern

Configuration

Option Name	Description
host	host string for the metrics server. Defaults to 127.0.0.1
port	port that metrics server listens on. Defaults to 9991
urlPatternMaker	function to create the url pattern matcher, defaults to (path) => new UrlPattern(path, { segmentNameCharset: "a-zA-Z0-9_-" })
normalizePath	boolean. Set this to false to use the original url instead of cleaned up ones.
createServer	boolean. Set this to false to not create the exporter server endpoint

Sample Output

When program starts, you will see the following:

Metrics server listening on 127.0.0.1:9991

Assuming you have a couple of routes defined like this:

// maps to /api/sub/:id/more/:id2
app.use("/api/sub", require("./sub_module"));

app.get("/api", (req, res) => {
  res.status(200).send("Api Works.");
});
app.get("/api/fast/", (req, res) => {
  res.status(200).send("Fast response!");
});
app.get("/api/slow", (req, res) => {
  setTimeout(() => {
    res.status(200).send("Slow response...");
  }, 1000);
});

app.get("/api/error", (req, res, next) => {
  try {
    throw new Error("Something broke...");
  } catch (error) {
    res.status(500).send(error.message);
  }
});

And you hit the corresponding routes in Postman or Curl. Check console again, you should see:

$ node src/main.js
Server is running on port 4000
Metrics server listening on 127.0.0.1:9991
Route found: /api/sub/:id
Route found: /api/sub/:id/more/:id2
Route found: /api
Route found: /api/fast
Route found: /api/slow
Route found: /api/error
Route found: /api/list/:listId

Navigate to 127.0.0.1:9991/metrics, you will see:

# HELP http_request_duration_seconds duration histogram of http responses labeled with: status_code, method, path
# TYPE http_request_duration_seconds histogram
http_request_duration_seconds_bucket{le="0.03",status_code="500",method="GET",path="/api/error"} 1
http_request_duration_seconds_bucket{le="0.3",status_code="500",method="GET",path="/api/error"} 1
http_request_duration_seconds_bucket{le="1",status_code="500",method="GET",path="/api/error"} 1
http_request_duration_seconds_bucket{le="1.5",status_code="500",method="GET",path="/api/error"} 1
http_request_duration_seconds_bucket{le="3",status_code="500",method="GET",path="/api/error"} 1
http_request_duration_seconds_bucket{le="5",status_code="500",method="GET",path="/api/error"} 1
http_request_duration_seconds_bucket{le="10",status_code="500",method="GET",path="/api/error"} 1
http_request_duration_seconds_bucket{le="+Inf",status_code="500",method="GET",path="/api/error"} 1
http_request_duration_seconds_sum{status_code="500",method="GET",path="/api/error"} 0.008067119
http_request_duration_seconds_count{status_code="500",method="GET",path="/api/error"} 1
http_request_duration_seconds_bucket{le="0.03",status_code="200",method="GET",path="/api/sub/:id/more/:id2"} 1
http_request_duration_seconds_bucket{le="0.3",status_code="200",method="GET",path="/api/sub/:id/more/:id2"} 1
http_request_duration_seconds_bucket{le="1",status_code="200",method="GET",path="/api/sub/:id/more/:id2"} 1
http_request_duration_seconds_bucket{le="1.5",status_code="200",method="GET",path="/api/sub/:id/more/:id2"} 1
http_request_duration_seconds_bucket{le="3",status_code="200",method="GET",path="/api/sub/:id/more/:id2"} 1
http_request_duration_seconds_bucket{le="5",status_code="200",method="GET",path="/api/sub/:id/more/:id2"} 1
http_request_duration_seconds_bucket{le="10",status_code="200",method="GET",path="/api/sub/:id/more/:id2"} 1
http_request_duration_seconds_bucket{le="+Inf",status_code="200",method="GET",path="/api/sub/:id/more/:id2"} 1
http_request_duration_seconds_sum{status_code="200",method="GET",path="/api/sub/:id/more/:id2"} 0.001186646
http_request_duration_seconds_count{status_code="200",method="GET",path="/api/sub/:id/more/:id2"} 1

# HELP up 1 = up, 0 = not up
# TYPE up gauge
up 1

To see how to visualize the data in prometheus+grafana, you can check out Node.js Monitoring with Prometheus+Grafana

Happy monitoring!

License

MIT