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Hello World - Shell
This guide describes the steps required to create the helloworld-shell
sample app and deploy it to your
cluster.
The sample app reads a TARGET
environment variable, and prints Hello ${TARGET}!
.
If TARGET
is not specified, World
is used as the default value.
You can also download a working copy of the sample, by running the following commands:
git clone -b "master" https://github.com/knative/docs knative-docs
cd knative-docs/docs/serving/samples/hello-world/helloworld-shell
Prerequisites
- A Kubernetes cluster with Knative installed and DNS configured. Follow the installation instructions.
- Docker installed and running on your local machine, and a Docker Hub account configured.
- Optional: You can use the Knative CLI client
kn
to simplify resource creation and deployment. Alternatively, you can usekubectl
to apply resource files directly.
Building
- Create a new file named
script.sh
and paste the script below. This will run BusyBox’http
returning a friendly welcome message asplain/text
plus some extra information:
#!/bin/sh
# Print out CGI header
# See https://tools.ietf.org/html/draft-robinson-www-interface-00
# for the full CGI specification
echo -e "Content-Type: text/plain\n"
# Use environment variable TARGET or "World" if not set
echo "Hello ${TARGET:=World}!"
# In this script you can perform more dynamic actions, too.
# Like printing the date, checking CGI environment variables, ...
-
Create a new file named
Dockerfile
and copy the code block below into it.# Busybox image that contains the simple 'httpd' # https://git.busybox.net/busybox/tree/networking/httpd.c FROM busybox # Serve from this directory WORKDIR /var/www # Prepare httpd command for being started via init # This indirection is required for proper SIGTERM handling RUN echo "::sysinit:httpd -vv -p 8080 -u daemon -h /var/www" > /etc/inittab # Copy over our CGI script and make it executable COPY --chown=daemon:daemon script.sh cgi-bin/index.cgi RUN chmod 755 cgi-bin/index.cgi # Startup init which in turn starts httpd CMD init
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
Deploying
-
After the build has completed and the container is pushed to Docker Hub, you can deploy the app into your cluster.
-
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"
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
With
kn
you can deploy the service withkn service create helloworld-shell --image=docker.io/{username}/helloworld-shell --env TARGET="Shell Sample v1"
This will wait until your service is deployed and ready, and ultimately it will print the URL through which you can access the service.
The output will look like:
Creating service 'helloworld-shell' in namespace 'default': 0.035s The Configuration is still working to reflect the latest desired specification. 0.139s The Route is still working to reflect the latest desired specification. 0.250s Configuration "helloworld-shell" is waiting for a Revision to become ready. 8.040s ... 8.136s Ingress has not yet been reconciled. 8.277s unsuccessfully observed a new generation 8.398s Ready to serve. Service 'helloworld-shell' created to latest revision 'helloworld-shell-kwdpt-1' is available at URL: http://helloworld-shell.default.1.2.3.4.xip.io
During the creation of your service, Knative performs the following steps:
- Creates of a new immutable revision for this version of the app.
- Programs the network to create a route, ingress, service, and load balance for your app.
- Automatically scales your pods up and down (including to zero active pods).
-
Verification
-
Run one of the followings commands 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
kn service describe helloworld-shell -o url
Example:
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.
Example:
curl http://helloworld-shell.default.1.2.3.4.xip.io Hello Shell Sample v1! # Even easier with kn: curl $(kn service describe helloworld-shell -o url)
Note: Add
-v
option to get more details if thecurl
command failed.
Removing
To remove the sample app from your cluster, delete the service record.
kubectl delete --filename service.yaml
kn service delete helloworld-shell
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