Content-type error since using Prometheus 3

[soso-bc]

Hello,

Upgrading to Prometheus 3, I encountered a content-type issue.
Prometheus expects 'text/plain' while the plugin returns 'text/html'

I fixed it locally but I think I would not be the only one.
That's why I give the correction:

$ grep -n 'register[;.]' Docker/plugins/zwavejs-prom/index.js
5:const register = promCli.register;
81: res.set('Content-Type', register.contentType);

[TheAceMan]

I ran into this as well. Could you explain your work around?

[soso-bc]

@TheAceMan
Modify the zwavejs-prom/index.js file to add the 2 lines (At line 5 and 81) returned by the grep command I specified.

[TheAceMan]

Ahh, thanks. Didn't realize the grep was ran after the change to show the modifications. Got it working. But this work around will be cleared on pod restart in the kubernetes cluster. Will have to look into a init container or some persistence if this is not going to be fixed.

[soso-bc]

You just need to create your own docker image by overloading the initial one.
ex:

FROM zwavejs/zwave-js-ui:latest

COPY plugins/zwavejs-prom/index.js /usr/src/app/node_modules/@kvaster/zwavejs-prom/index.js

[TheAceMan]

A bit hackish but the init container is working. Creating a image would require a container registry and pushing new images as zwave-js-ui base updates. Got it all working and hopefully it's a short term.

[kvaster]

Fixed by #6

[joneshf]

Ran into this as well. The migration guide for Prometheus actually calls this failure out: https://prometheus.io/docs/prometheus/latest/migration/#scrape-protocols.

If you cannot update to a version of @kvaster/zwavejs-prom that fixes this (like me) there's another option in that guide: set the fallback_scrape_protocol explicitly.

E.g. If you're running this in k8s (which, surprisingly someone else in this thread seems to be doing!) and using the Prometheus Operator (or at least their CRDs), you can set fallbackScrapeProtocol on your *Monitor:

 apiVersion: monitoring.coreos.com/v1
 kind: ServiceMonitor
 metadata:
   name: z-wave-js
   namespace: z-wave-js
 spec:
   endpoints:
     - path: /metrics
       port: ui
+  fallbackScrapeProtocol: PrometheusText1.0.0
   selector:
     matchLabels:
       app.kubernetes.io/component: z-wave-js
       app.kubernetes.io/name: z-wave-js

Or whatever.

You should be able to do similar with the fallback_scrape_protocol in plain old Prometheus files if you're doing it that way as well.

---

And for the sake of SEO for the next person that runs into this, the error I was receiving looked something like this:

Error scraping target: received unsupported Content-Type "text/html; charset=utf-8" and no fallback_scrape_protocol specified for target