Expose metric endpoint for prometheus

kongzii · April 4, 2020, 1:48pm

Hi,

I am trying to expose metrics for Prometheus but I could not find any resources about how to do this. Is there any documentation or example code?

Thanks.

johannesweiss · April 5, 2020, 1:47pm

Did you try SwiftPrometheus which is a backend for SwiftMetrics. I'm sure the author @MrLotU is also happy to help if you have questions/issues.

kongzii · April 6, 2020, 1:21pm

I was looking into both. But I could not find any documentation about how to integrate it into Vapor. I wanted to measure response time per endpoint and expose it via /metrics endpoint but without any luck so far.

johannesweiss · April 14, 2020, 11:27am

I see! @tanner0101 and @MrLotU any pointers on how to integrate with Vapor?

MrLotU · April 14, 2020, 11:34am

Vapor 4 uses swift-metrics by default. To add a /metrics endpoint you can add the following route:

    app.get("metrics") { req -> EventLoopFuture<String> in
        let promise = req.eventLoop.makePromise(of: String.self)
        try MetricsSystem.prometheus().collect(into: promise)
        return promise.futureResult
    }

This will return the prometheus metrics, given you have bootstrapped MetricsSystem with Prometheus like so:

let myProm = PrometheusClient()
MetricsSystem.bootstrap(myProm)

See also: GitHub - swift-server-community/SwiftPrometheus: Client side Prometheus library in Swift

tanner0101 · April 14, 2020, 2:26pm

Vapor collects the follow metrics by default:

http_requests_total (counter)
http_request_errors_total (counter)
http_request_duration_seconds (timer)

github.com

vapor/vapor/blob/main/Sources/Vapor/Responder/DefaultResponder.swift#L83-L107


      
                          for: request,
                          startTime: startTime,
                          statusCode: status.code
                      )
                  }
              }
          }
          
          
/// Gets a `Route` from the underlying `TrieRouter`.
          private func getRoute(for request: Request) -> CachedRoute? {
              let pathComponents = request.url.path
                  .split(separator: "/")
                  .map(String.init)
              
              // If it's a HEAD request and a HEAD route exists, return that route...
              if request.method == .HEAD, let route = self.router.route(
                  path: [HTTPMethod.HEAD.string] + pathComponents,
                  parameters: &request.parameters
              ) {
                  return route

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kongzii · April 15, 2020, 10:07am

Thank you all. Now it works :)

stepanulyanin · August 19, 2021, 8:15pm

Hi, sorry for a dumb question, but how would one access these?

ktoso · August 20, 2021, 1:47am

Depends what you mean by "access" but generally the way to use metrics is to configure a specific backend for GitHub - apple/swift-metrics: A Metrics API for Swift (the readme lists a few), and then metrics emitted by any framework will show up in the backend of your choice.

For prometheus specifically, you'd use GitHub - swift-server-community/SwiftPrometheus: Client side Prometheus library in Swift

stepanulyanin · August 21, 2021, 1:34am

Ok great, thank you for the explanation! I thought that some of these are automatically available in Vapor without SwiftMetrics.