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Hello World - Shell
A simple web app that executes a shell script. The shell script reads an env
variable TARGET
and prints Hello ${TARGET}!
. If the TARGET
environment
variable is not specified, the script uses World
.
Follow the steps below to create the sample code and then deploy the app to your cluster. You can also download a working copy of the sample, by running the following commands:
git clone -b "{{< branch >}}" https://github.com/knative/docs knative-docs
cd knative-docs/docs/serving/samples/hello-world/helloworld-shell
Before you begin
- A Kubernetes cluster with Knative installed and DNS configured. Follow the installation instructions if you need to create one.
- Docker installed and running on your local machine, and a Docker Hub account configured (we’ll use it for a container registry).
Recreating the sample code
-
Create a new file named
script.sh
and paste the following script:#!/bin/sh echo Hello ${TARGET:=World}!
-
Create a new file named
invoke.go
and paste the following code. We use a basic web server written in Go to execute the shell script:package main import ( "fmt" "log" "net/http" "os" "os/exec" ) func handler(w http.ResponseWriter, r *http.Request) { log.Print("helloworld: received a request") cmd := exec.CommandContext(r.Context(), "/bin/sh", "script.sh") cmd.Stderr = os.Stderr out, err := cmd.Output() if err != nil { w.WriteHeader(500) } w.Write(out) } func main() { log.Print("helloworld: starting server...") http.HandleFunc("/", handler) port := os.Getenv("PORT") if port == "" { port = "8080" } log.Printf("helloworld: listening on %s", port) log.Fatal(http.ListenAndServe(fmt.Sprintf(":%s", port), nil)) }
-
Create a new file named
Dockerfile
and copy the code block below into it.# Use the official Golang image to create a build artifact. # This is based on Debian and sets the GOPATH to /go. # https://hub.docker.com/_/golang FROM golang:1.13 as builder # Create and change to the app directory. WORKDIR /app # Retrieve application dependencies using go modules. # Allows container builds to reuse downloaded dependencies. COPY go.* ./ RUN go mod download # Copy local code to the container image. COPY invoke.go ./ # Build the binary. # -mod=readonly ensures immutable go.mod and go.sum in container builds. RUN CGO_ENABLED=0 GOOS=linux go build -mod=readonly -v -o server # Use the official Alpine image for a lean production container. # https://hub.docker.com/_/alpine # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds FROM alpine:3 RUN apk add --no-cache ca-certificates # Copy the binary to the production image from the builder stage. COPY --from=builder /app/server /server COPY script.sh ./ # Run the web service on container startup. CMD ["/server"]
-
Create a new file,
service.yaml
and copy the following service definition into the file. Make sure to replace{username}
with your Docker Hub username.apiVersion: serving.knative.dev/v1 kind: Service metadata: name: helloworld-shell namespace: default spec: template: spec: containers: - image: docker.io/{username}/helloworld-shell env: - name: TARGET value: "Shell Sample v1"
-
Use the go tool to create a
go.mod
manifest.go mod init github.com/knative/docs/docs/serving/samples/hello-world/helloworld-shell
Building and deploying the sample
Once you have recreated the sample code files (or used the files in the sample folder) you’re ready to build and deploy the sample app.
-
Use Docker to build the sample code into a container. To build and push with Docker Hub, run these commands replacing
{username}
with your Docker Hub username:# Build the container on your local machine docker build -t {username}/helloworld-shell . # Push the container to docker registry docker push {username}/helloworld-shell
-
After the build has completed and the container is pushed to docker hub, you can deploy the app into your cluster. Ensure that the container image value in
service.yaml
matches the container you built in the previous step. Apply the configuration usingkubectl
:kubectl apply --filename service.yaml
-
Now that your service is created, Knative performs the following steps:
- Create a new immutable revision for this version of the app.
- Network programming to create a route, ingress, service, and load balance for your app.
- Automatically scale your pods up and down (including to zero active pods).
-
Run the following command to find the domain URL for your service:
kubectl get ksvc helloworld-shell --output=custom-columns=NAME:.metadata.name,URL:.status.url
Example:
NAME URL helloworld-shell http://helloworld-shell.default.1.2.3.4.xip.io
-
Now you can make a request to your app and see the result. Replace the URL below with the URL returned in the previous command.
curl http://helloworld-shell.default.1.2.3.4.xip.io
Example:
curl http://helloworld-shell.default.1.2.3.4.xip.io Hello Shell Sample v1!
Note: Add
-v
option to get more detail if thecurl
command failed.
Removing the sample app deployment
To remove the sample app from your cluster, delete the service record:
kubectl delete --filename service.yaml
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