Koa middleware doesn't return stats on /metrics if your aplication has a default handler

[maherma-adg]

My application has a default handler to catch any request not fullfilled by previous middlewares (koa-static, koa-routes) in order log those requests and return a custom 404 page.

After install prometheus-api-metrics, I was surprised when request on /metrics and /metrics.json url are logged by the default handler.

Looking into middleware function I think there is a error because after fulfill the /metrics and /metrics.json queries, the function call next() to drill down on middleware chain. IMHO request must be finished in this point, don't propagate the request and return the stats.

As workaround, you can define these paths in your router and do nothing. This allow the response generated by the middleware to be returned and not be overwritten by default handler.

router.get('/metrics', async (ctx) => {})
router.get('/metrics.json', async (ctx) => {})

Regards,
Manuel

[kobik]

@maherma-adg , thanks for reporting this.

I agree that for /metrics endpoint, next should not be called in when using Koa