'linkerd routes' command doesn't show anything when running with low value of time window option

[nfsp3k]

linkerd routes doesn't show anything when I set the value of -t option relatively low.
For example, a load generator sends 300RPS workload and the output of linkerd routes is as follows when the value of -t option is:
'10s'

'15s' (RPS is unstable and varies.)

'20s'

'30s'

I configured Linkerd-Prometheus to scrape metrics every second as follows:

Actually, linkerd routes works perfectly with the low value of -t option (e.g., 2s) some days ago, but it doesn't work correctly now and I don't know the reason.

The current environment of mine is as follows:

• Linkerd version: v2.8.1
• K8S version: v1.17.9
• CNI: Calico
• Other components deployed together: Jaeger, Prometheus-adapter, Linkerd Service Profile

I think it would be a poor question but I am new to Linkerd and I hope you understand.
Thanks in advance.

[cpretzer]

Hi @nfsp3k the -t flag specifies the time window that the routes command uses when it generates the prometheus query to show the metrics. You can see the prometheus queries that are generated by setting -log-level=debug in the linkerd-controller deployment.

Here's an example that I generated from our emojivoto application:

histogram_quantile(0.95, sum(irate(route_response_latency_ms_bucket{direction="inbound", dst=~"(web-svc.emojivoto.svc.cluster.local)(:\\d+)?", namespace="emojivoto"}[10s])) by (le, dst, rt_route))

The query uses the value specified by -t in the prometheus irate function, so the query is for the route_response_latency_ms_bucket last two data points looking 10 seconds back. It's entirely possible that there are no data points, which is why you are seeing no values.

I ran watch linkerd routes svc/web-svc -t 10s and eventually some results would display. If you get the queries from the -log-level=debug output of the linkerd-controller you can access the prometheus query UI with kubectl port-forward svc/linkerd-prometheus -n linkerd 9090 and run the queries there to see what is displayed.