9.9.1 Build a container image
Dockerfile.Task 9.9.1.1: Build a container image
The build can be done using any container building tool that supports Dockerfile builds.
The sample application is an HTTP server written in the Go programming language .
The following files are needed inside your application repository:
Sample go application
This Go code defines an HTTP server listening on port 8080. It has to be placed in the main.go file.
package main
import (
"fmt"
"net/http"
)
func main() {
http.HandleFunc("/", HelloServer)
http.ListenAndServe(":8080", nil)
}
func HelloServer(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(w, "Hello, %s!", r.URL.Path[1:])
}
Calling this app will return “Hello,” followed by the given path.
Examples:
| url | response |
|---|---|
| localhost:8080/ | Hello, ! |
| localhost:8080/world | Hello, world! |
| localhost:8080/appuio | Hello, appuio! |
Image build instruction
The Dockerfile defines the image build (Dockerfile reference
).
FROM registry.access.redhat.com/ubi8/go-toolset:1.24.6-1759234265 AS build
COPY main.go /opt/app-root/src
ENV CGO_ENABLED=0\
GOOS=linux\
GOARCH=amd64\
GO111MODULE=off
RUN go build -a -o go-hello-world-app .
FROM registry.access.redhat.com/ubi8/ubi:8.10-1756195303
RUN useradd -ms /bin/bash golang
RUN chgrp -R 0 /home/golang && \
chmod -R g+rwX /home/golang
USER golang
COPY --from=build /opt/app-root/src/go-hello-world-app /home/golang/
EXPOSE 8080
CMD /home/golang/go-hello-world-app
It is a multi-stage build . The build is done in several stages using different containers.
- use a Go container to build the Go application
- copy the go binary from the build to a minimal ubi image Universal Base Image
Note
Multi-stage builds have two major advantages; smaller image size and higher security. The resulting image does only contain the minimal set of required packages. This reduces the image size and increases security (smaller attack surface).Image build
The image build is shown using Buildah . Buildah - a tool that facilitates building OCI container images.
Find Docker instructions hint at the bottom of this page or under Docker Instructions .
Buildah build command:
buildah bud -f Dockerfile -t go-hello-world .
The image is available locally:
buildah images
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/go-hello-world latest 7f3ed9de1e49 3 seconds ago 219 MB
registry.access.redhat.com/ubi8/ubi 8.2 7923da9ba983 6 days ago 212 MB
registry.access.redhat.com/ubi8/go-toolset 1.13.4 4bf10ac637aa 5 weeks ago 990 MB
Image test
Test the container image locally using Podman . Use this command to run the container:
podman run -p 8088:8080 -ti localhost/go-hello-world
This makes the Go application accessible by the port 8088 of your device.
It can be tested with a browser (http://localhost:8088/world ) or using curl:
curl localhost:8088/world
Publish image to Docker Hub
To make the image accessible to OpenShift, it must be pushed to an image registry. We use Docker Hub as the registry.
podman login
podman push localhost/go-hello-world:latest docker://docker.io/appuio/go-hello-world:latest