[New builder] Introduce Cancelot

.gitignore

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+.idea

cancelot/Dockerfile

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+FROM gcr.io/cloud-builders/go AS build-env
+
+ADD ./ /go/src/
+
+ENV GOBIN=/go/bin
+RUN go get -d -v ./...
+RUN go install /go/src/main.go
+
+FROM alpine:latest
+
+RUN apk add --no-cache ca-certificates
+
+COPY --from=build-env /go/bin/main /go/bin/main
+
+ENTRYPOINT [ "/go/bin/main" ]

cancelot/README.md

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+# Cancelot
+
+Cancelot (thank you Twitter for the name :D) allows you to cancel previous builds running for the same branch, 
+when you are using VCS triggered builds.
+
+# Purpose
+
+Cancelot was built because there is no out of the box solution by CloudBuild, in order to cancel a previous running 
+build upon a new commit in the same branch. This can save a lot of build minutes that would be otherwise billed to the 
+account.
+
+# Deploying Cancelot
+
+* Make any changes you need
+* Navigate to Cancelot's folder and execute the following: `gcloud builds submit . --config=cloudbuild.yaml`
+* Enjoy
+
+## Using Cancelot
+
+Add the builder as the first step in your project's `cloudbuild.yaml`:
+
+```yaml
+steps:
+- name: 'gcr.io/$PROJECT_ID/cancelot'
+  args: [ 
+    '--current_build_id', '$BUILD_ID',
+    '--branch_name', '$BRANCH_NAME'
+  ]
+```
+
+Cancelot will be invoked when your build starts and will try to find any running jobs that match the following filter:
+
+```
+build_id != "[CURRENT_BUILD_ID]" AND 
+source.repo_source.branch_name = "[BRANCH_NAME]" AND 
+status = "WORKING" AND 
+start_time<"[CURRENT_BUILD_START_TIME]"
+```
+
+After successfully fetching the list with the running builds that match the defined criteria, it loops and cancels 
+each one.
+
+## Inspiration
+
+Cancelot is heavily inspired by `slackbot` from CloudBuilders community

cancelot/cancelot/cancelpreviousbuild.go

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+package cancelot
+
+import (
+	"context"
+	"fmt"
+	"google.golang.org/api/cloudbuild/v1"
+	"log"
+)
+
+// Checks for previous running builds on the same branch, in order to cancel them
+func CancelPreviousBuild(ctx context.Context, currentBuildId string, branchName string) {
+	svc := gcbClient(ctx)
+	project, err := getProject()
+	if err != nil {
+		log.Fatalf("Failed to get project: %v", err)
+	}
+
+	log.Printf("Going to fetch current build details for: %s", currentBuildId)
+
+	currentBuildResponse, currentBuildError := svc.Projects.Builds.Get(project, currentBuildId).Do()
+	if currentBuildError != nil {
+		log.Fatalf("Failed to get build details from Cloud Build.  Will retry in one minute.")
+	}
+
+	log.Printf("Going to check ongoing jobs for branch: %s", branchName)
+
+	onGoingJobFilter := fmt.Sprintf(`
+		build_id != "%s" AND 
+		source.repo_source.branch_name = "%s" AND 
+		status = "WORKING" AND 
+		start_time<"%s"`,
+		currentBuildId,
+		branchName,
+		currentBuildResponse.StartTime)
+
+	log.Printf("Builds filter created: %s", onGoingJobFilter)
+
+	onGoingBuildsResponse, onGoingBuildsError := svc.Projects.Builds.List(project).Filter(onGoingJobFilter).Do()
+
+	if onGoingBuildsError != nil {
+		log.Fatalf("Failed to get builds from Cloud Build.  Will retry in one minute.")
+	}
+
+	onGoingBuilds := onGoingBuildsResponse.Builds
+	numOfOnGoingBuilds := len(onGoingBuilds)
+
+	log.Printf("Ongoing builds for %s has size of: %d", branchName, numOfOnGoingBuilds)
+
+	if numOfOnGoingBuilds == 0 {
+		return
+	}
+
+	for _, build := range onGoingBuilds {
+		log.Printf("Going to cancel build with id: %s", build.Id)
+
+		cancelBuildCall := svc.Projects.Builds.Cancel(project, build.Id, &cloudbuild.CancelBuildRequest{})
+		buildCancelResponse, buildCancelError := cancelBuildCall.Do()
+
+		if buildCancelError != nil {
+			log.Fatalf("Failed to cancel build with id:%s - %v", build.Id, buildCancelError)
+		}
+
+		log.Printf("Cancelled build with id:%s", buildCancelResponse.Id)
+	}
+}

cancelot/cancelot/cloudbuild.go

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+package cancelot
+
+import (
+	"bytes"
+	"context"
+	"log"
+	"os/exec"
+	"strings"
+
+	"cloud.google.com/go/compute/metadata"
+	"golang.org/x/oauth2/google"
+	cloudbuild "google.golang.org/api/cloudbuild/v1"
+)
+
+// getProject gets the project ID.
+func getProject() (string, error) {
+	// Test if we're running on GCE.
+	if metadata.OnGCE() {
+		// Use the GCE Metadata service.
+		projectID, err := metadata.ProjectID()
+		if err != nil {
+			log.Printf("Failed to get project ID from instance metadata")
+			return "", err
+		}
+		return projectID, nil
+	}
+	// Shell out to gcloud.
+	cmd := exec.Command("gcloud", "config", "get-value", "project")
+	var out bytes.Buffer
+	cmd.Stdout = &out
+	err := cmd.Run()
+	if err != nil {
+		log.Printf("Failed to shell out to gcloud: %+v", err)
+		return "", err
+	}
+	projectID := strings.TrimSuffix(out.String(), "\n")
+	return projectID, nil
+}
+
+func gcbClient(ctx context.Context) *cloudbuild.Service {
+	client, err := google.DefaultClient(ctx, cloudbuild.CloudPlatformScope)
+	if err != nil {
+		log.Fatalf("Caught error creating client: %v", err)
+	}
+	svc, err := cloudbuild.New(client)
+	if err != nil {
+		log.Fatalf("Caught error creating service: %v", err)
+	}
+	return svc
+}

cancelot/cloudbuild.yaml

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+steps:
+- name: 'gcr.io/cloud-builders/docker'
+  args: [ 'build', '-t', 'gcr.io/$PROJECT_ID/cancelot', '.' ]
+images:
+- 'gcr.io/$PROJECT_ID/cancelot'
+tags: ['cloud-builders-community']

cancelot/main.go

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+// Post build status results to Slack.
+
+package main
+
+import (
+	"context"
+	"flag"
+	"log"
+
+	"./cancelot"
+)
+
+var (
+	currentBuildId = flag.String("current_build_id", "", "The current build id, in order to be excluded")
+	branchName     = flag.String("branch_name", "", "BranchName to cancel previous ongoing jobs on")
+)
+
+func main() {
+	log.Print("Starting cancelot")
+	flag.Parse()
+	ctx := context.Background()
+
+	if *currentBuildId == "" {
+		log.Fatalf("CurrentBuildId must be provided.")
+	}
+
+	if *branchName == "" {
+		log.Fatalf("BranchName must be provided.")
+	}
+
+	cancelot.CancelPreviousBuild(ctx, *currentBuildId, *branchName)
+	return
+}