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Starting Docker with
Golang
Go Conference 2018 Spring
@sakajunquality
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Are you using Docker?
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Probably Yes
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Using docker for...
- Building a Go app
- Running a Go app
- Developing a Go app
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Probably you know
difference between
container and virtualization?
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Container and VM
- https://www.docker.com/what-container#/virtual_machines
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Let’s just say that
containers are less overhead
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(Generally speaking)
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What’s Container?
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Container is...
- Using linux namespace, separate resources, like CPU, Memory, File System
etc. for each process
- Docker is a one implementation of container
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What’s Docker?
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Docker is...
- A runtime for application using container
https://www.docker.com/what-docker
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Docker ≠ Container
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containerd and runC
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- Runtime engine for docker
- Used to be within Docker
containerd and runC
https://containerd.io/
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containerd and runC
https://containerd.io/
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Forget this for now
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containerd and runC in a nutshell
Docker / moby
containerd
runC Linux Kernel
(cgroup etc.)
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containerd and runC in a nutshell
Docker / moby
containerd
runC
OCI standard
Something else
(maybe)
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$ go get github.com/opencontainers/runc
$ cd $GOPATH/src/github.com/opencontainers/runc
$ make // compile
$ sudo make install // path
Install runC
Note: tested on arch linux
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$ mkdir ~/mygolangcontainer
$ cd ~/mygolangcontainer
$ mkdir rootfs
$ docker export $(docker create golang:1.10.1) | tar -C rootfs -xvf -
$ runc spec
$ vim config.json // add PATH /go/bin:/usr/local/go/bin
$ sudo runc run mygolangcontainer
# which go
/usr/local/go/bin/go
# go
Go is a tool for managing Go source code.
...
Run container without docker
Note: tested on arch linux
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You can run container without docker
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You can embed container into
application
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Implementation example in golang
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:dogeza:
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but
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contained has plenty of examples
https://github.com/containerd/containerd
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and
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Container is made of golang (almost)
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Almost
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Let’s go back to the real world
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Most of us will not use
container directly
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Tips for Running and Building
Golang app in Docker
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Take a look at Dockerhub Golang
https://hub.docker.com/_/golang/
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package main
import (
"fmt"
"net/http"
)
func handler(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(w, "GoCon 2018 Spring")
}
func main() {
http.HandleFunc("/", handler)
http.ListenAndServe(":8888", nil)
}
Using simple http app
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Let’s follow the official example
FROM golang:1.10.1
WORKDIR /go/src/github.com/sakajunquality/hello-go-docker
COPY main.go main.go
RUN go get -d -v ./...
RUN go install -v ./...
CMD ["hello-go-docker"]
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It works
$ docker build --no-cache --rm -t hello-docker:v1 .
$ docker run -d -p 8888:8888 hello-docker:v1
$ curl localhost:8888
> GoCon 2018 Spring
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But the image is too big
$ docker images | grep hello-docker
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-docker v1 77867ff7da90 About an hour ago 787MB
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Let’s use alpine
FROM golang:1.10.1-alpine
WORKDIR /go/src/github.com/sakajunquality/hello-go-docker
COPY main.go main.go
RUN go get -d -v ./...
RUN go install -v ./...
CMD ["hello-go-docker"]
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Still the image is big
$ docker images | grep hello-docker
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-docker v2 6b84ba9a4a72 About an hour ago 382MB
hello-docker v1 77867ff7da90 About an hour ago 787MB
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Why?
$ docker images | grep golang
REPOSITORY TAG IMAGE ID CREATED SIZE
golang 1.10.1-alpine 52d894fca6d4 2 days ago 376MB
golang 1.10.1 6fe15d4cbc64 2 weeks ago 780MB
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Diff
$ docker images | grep golang
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-docker v2 6b84ba9a4a72 About an hour ago 382MB
golang 1.10.1-alpine 52d894fca6d4 2 days ago 376MB
hello-docker v1 77867ff7da90 About an hour ago 787MB
golang 1.10.1 6fe15d4cbc64 2 weeks ago 780MB
6MB
7MB
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For running golang app
- Golang itself is not required
- Source code is also not required
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Separate build image and runtime image
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Let’s use multi stage build
FROM golang:1.10.1-alpine as build
WORKDIR /go/src/github.com/sakajunquality/hello-go-docker
COPY main.go main.go
RUN go get -d -v ./...
RUN go install -v ./...
FROM alpine
RUN apk add --no-cache ca-certificates
COPY --from=build /go/bin/hello-go-docker /usr/local/bin/hello-go-docker
CMD ["hello-go-docker"]
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Finally the image is small enough
$ docker images | grep hello-docker
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-docker v3 a5048da4d653 23 minutes ago 11.3MB
hello-docker v2 6b84ba9a4a72 About an hour ago 382MB
hello-docker v1 77867ff7da90 About an hour ago 787MB
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If you need a more small image...
- https://github.com/tetsu-koba/minimumgo
$ docker export $(docker create alpine) | tar -C rootfs -xvf -ls
$ ls rootfs
bin dev etc home lib media mnt proc root run sbin srv sys tmp usr var
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If you need a static build...
FROM golang:1.10.1-alpine as build
…
RUN go install
…
FROM node:9 as static-build
…
RUN yarn install
…
FROM alpine
…
COPY --from=build /go/bin/myapp /usr/local/bin/myapp
COPY --from=build-static /path/to/myapp/static /usr/local/src/myapp/static
CMD ["myapp"]
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Conclusion
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<3
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Thank you