Port forward a service

[AlbertoSoutullo]

I would like to know if there is a way to get a service, and create a port forward to my local machine. I saw that his can be done pretty easily with external libraries, but I would like to stick with only one K8s library.

My idea is to forward whatever Thanos pod is available through it's service to my local machine, and then make queries to download some metrics to analyze them locally.

Looking at the documentation and other issues, like pod_porforward.py or #2138, but those couldn't really help me, since they are specific to pods, and I would like to do it through a service.

Is there a way to do this? Or I am not completely understanding the documentation?

Regards.

[roycaihw]

/assign @iciclespider

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[iciclespider]

@AlbertoSoutullo, use the kubernetes apis to obtain the service and then search for a pod that matches the port you are trying to attach to. This is exactly what the kubectl cli does behind the scenes. The example you linked to also does exactly that here: https://github.com/kubernetes-client/python/blob/master/examples/pod_portforward.py#L143-L171

[AlbertoSoutullo]

@iciclespider That makes perfect sense now that I think about it. Thank you very much! I will try this and if I find any problem I will reopen this.

[matthewfischl]

@AlbertoSoutullo did you find a solution that worked for you? If so, would you mind sharing?

Not sure if our goals are the same, but I am currently using port forwarding to enable local testing of an API.

For example, PRIOR to running a python request to an API, I would need to do the following (I started doing this in a command line then shifted to executing these with a python subprocess):

1. aws eks update-kubeconfig --region us-east-1 --name
2. kubectl port-forward service/ : -n
3. Then make a request in python like: request.get("http://localhost:local port")

However, this approach would require running kubectl for EVERY service that I would want to forward AND doing this with python subprocesses seems undesirable (at least how I implemented it!)

So, ultimately I am trying to replace step #2 with something from the Kubernetes client library. I was hoping that doing so would provide a localhost url that requests could be sent to. However, I'm not exactly sure if that is what the Kubernetes library is designed for?

So, are you trying to do something similar? Any thoughts? Thanks!

[iciclespider]

@matthewfischl The port forwarding ability of the python client does exactly what your step 2 is doing. Here is an example of your step 2, but just in the python code: https://github.com/kubernetes-client/python/blob/master/examples/pod_portforward.py

[AlbertoSoutullo]

@AlbertoSoutullo did you find a solution that worked for you? If so, would you mind sharing?

Hello @matthewfischl ! I wanted to do what you mention in your message (I was hoping that doing so would provide a localhost url that requests could be sent to.).
What I implemented some time ago was something that helped me to keep advancing with what I wanted to do, but I am not still sure it is the “best” approach.

From my understanding, and also something that they comment at the beginning of the pod port forward example, is that the behavior is not exactly the same. I mean, you will not open a port where you can send request command to that address:port.

What you will do is monkey patch the create_connection function from socket. So basically, every time you do a request, this will automatically be called underneath, creating a connection to your Kubernetes cluster without the need of opening ports. Note that I had to use urllib_request.urlopen(request) instead of your request.get().

You can see my code, it is public:

• Here I am creating the function that will act inside urllib_request.urlopen(request).
• Here I am doing the monkey patch.
• Here is the function I use in the previous link, where I am querying Kubernetes.

An example of that request parameter would be something like:

http://thanos-query.svc.thanos.kubernetes:9090/api/v1/query_range?query=libp2p-peers&start=1715769060.0&end=1715770080.0&step=60s

I am using this to basically scrape a lot of metrics through Thanos, for which I have a service that cannot be access from outside the cluster unless you use a port forward, or this kind of approach. Then I just parse the data accordingly with what I want to do.

I hope this can help. Again, I am not sure if this is the optimal approach. Like you, I also had in mind something like "opening a local port where I can query with standard requests", but as far as I know, the port forward of this library doesn't work like that.

Let me know if I can help you with something else!