In the last article we dealt with command line tools. Kubectl is of course the be-all and end-all when administering the Kubernetes cluster. The program comes with many functions from home. But there is also a plugin feature that lets you do a lot more.
Curl as a command line tool for a wide variety of services, especially web services, has become an integral part of everyday life. Be it to check whether a web server is available and responding, or to quickly query something or download a file, all of this is done very quickly with curl. A curl -n demoapp http://demoapp-57bf45f76-bgkwb:8080/ usually does not work in the Kubernetes cluster, since a pod is only connected via the overlay network and the service network is only connected internally in the cluster functions. You would need an ingress or a service with NodePort or an external load balancer.
The solution to the dilemma is called Kubectl Curl. The plugin starts a port forward from a local port via the Kubernetes API to the target pod. The inventor then went to great lengths to process all curl options in the plugin as a Go package. Too much trouble I think, but it didn’t work in the Rancher environment. It had taken a while to figure that out. It then ended up in this fork, which on the one hand makes the package superfluous and then also works in rancher clusters.
The installation is very easy if you download a corresponding binary from the Release page and copy it to the same directory as kubectl. Anyone who has installed Go will also find a command for installing via Go in the README.
Prerequisite for use is a local curl. jq further refines the json output.
What can we do with kubectl-curl:
$ kubectl curl -n demoapp http://demoapp-57bf45f76-bgkwb:8080/
$ kubectl curl -n kube-logging http://kube-logging-logging-operator-f874c54f8-wcd6g:8080/metrics
$ kubectl curl -n cattle-monitoring-system http://prometheus-rancher-monitoring-prometheus-0:9090/api/v1/query?query=fluentbit_uptime | jq .
$ kubectl curl -n kube-system http://traefik-rmtth:9000/ping
Have a lot of fun!