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Debugging your first microservice

You can debug your application from the IDE or via the CLI.

IDEs

Command Line Interface

Prerequisites

  • A kubernetes cluster with kubectl configured.
  • Go, and DLV go debugger installed
  • Squash server, client and command line binary installed.
  • Docker repository that you can push images to, and that kubernetes can access (docker hub for example)

Verify

  • Kubectl port-forward functionality works.
  • You have access to the squash server - use $ squash --url=http://SQUASH-SERVER-ADDRESS/api/v2 list attachments to test that it is working properly.

If you have an issue with either, see the FAQ for help.

Build

In your favorite text editor, create a new main.go file. Here's the one we will be using in this tutorial:

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
)

type Calculator struct {
	Op1, Op2 int
	IsAdd    bool
}

func main() {
	http.HandleFunc("/calculate", calchandler)

	log.Fatal(http.ListenAndServe(":8080", nil))
}

func calchandler(w http.ResponseWriter, r *http.Request) {
	var req Calculator
	dec := json.NewDecoder(r.Body)
	err := dec.Decode(&req)
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
	}

	isadd := req.IsAdd
	op1 := req.Op1
	op2 := req.Op2

	if isadd {
		fmt.Fprintf(w, "%d", op1-op2)
	} else {
		fmt.Fprintf(w, "%d", op1+op2)
	}
}

Build a docker container

In the same folder as main.go add a Dockerfile:

FROM alpine
COPY microservice /microservice
ENTRYPOINT ["/microservice"]

EXPOSE 8080

To build everything conviently, you can add a Makefile (replace with the appropreate value):

microservice:
	GOOS=linux CGO_ENABLED=0 go build -gcflags "-N -l" -o microservice
	docker build -t <YOUR REPO HERE>/microservice:0.1 .
dist:
	docker push <YOUR REPO HERE>/microservice:0.1

CGo is disabled as it is not compatible with the alpine image. The gcflags part adds more debug information for the debugger.

Over all your directory should have three files so far:

  • Dockerfile
  • main.go
  • Makefile

Finally, execute

$ make microservice && make dist

to build and deploy the microservice.

Deploy the microservice to kubernetes.

Create a manifest for kubernetes named microservice.yml

apiVersion: v1
kind: ReplicationController
metadata:
  name: example-microservice-rc
spec:
  replicas: 1
  selector:
    app: example-microservice
  template:
    metadata:
      labels:
        app: example-microservice
    spec:
      containers:
      - name: example-microservice
        image: <YOUR REPO HERE>/microservice:0.1
        ports:
        - containerPort: 8080
          protocol: TCP
---
kind: Service
apiVersion: v1
metadata:
  name: example-microservice-svc
spec:
  selector:
    app: example-microservice
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080

and deploy it to kubernets:

$ kubectl create -f microservice.yml

Debug

Use kubectl to find the name of the pod you want to deubg. Then, Use the squash command line to request an attachment to a container.

$ squash --url=http://SQUASH-SERVER-ADDRESS/api/v2 debug-container <YOUR REPO HERE>/microservice:0.1 example-microservice-rc-n9x2r example-microservice dlv

Take the ID parameter from the response:

Debug config id: 1427131847

Then wait for the debugger to attach. Note - this command has a default timeout of 1 second, which may not be enough. If it times out, just run it again. If nothing happens after a minute or so, please contact us.

$ squash --url=http://SQUASH-SERVER-ADDRESS/api/v2 wait 1427131847
Debug session started! debug server is at: squash-client-56v2q.squash:33275

This address is a pod.namespace:port. To easly and securly access the debugger server's port, you can use kubectl port-forward:

$ kubectl port-forward --namespace squash squash-client-56v2q 33275
Forwarding from 127.0.0.1:33275 -> 33275
Forwarding from [::1]:33275 -> 33275

Leave it running in the background. Then just attach (your ports may vary)

$ dlv connect localhost:33275

If kubectl port-forward doesnt work for you or you can't access the sqash server from your laptop, check out our FAQ page.