Samarthya

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Dockeriz’d service

Saurabh Sharma 5 years ago

Someone asked me to define a simple docker pod for the service I wrote in GOLang here. I completely forgot about it, till today.

So here is my first attempt at getting a docker image for the service.

The code is available here.

My code space is organised as under, and I am using VS Code to write this docker file.

├── Dockerfile
├── README.MD
├── gqs.code-workspace
└── src
    ├── counter
    │   ├── count.go
    │   └── count.service.go
    ├── go.mod
    ├── server.go
    ├── user
    │   ├── user.data.go
    │   ├── user.go
    │   └── user.service.go
    └── users.json

Let me first publish my Dockerfile and then I will explain it.

# Building the container image for the image.
ARG VERSION=alpine

# Sets the base image
FROM golang:${VERSION} AS baseimage
RUN echo 'Building image...'

# Environment variable for the home directory
ENV home /server
WORKDIR ${home}

ADD ./src/counter/* ./counter/
ADD ./src/user/* ./user/
ADD ./src/server.go ./server.go
ADD ./src/go.mod ./go.mod
ADD ./src/users.json ./

RUN go build -o main server.go  

EXPOSE 8090
ENTRYPOINT [ "/server/main" ]

We start with the FROM using the golang:alpine image.

  • The ARG instruction defines a variable that users can pass at build-time to the builder with the docker build command using the --build-arg <varname>=<value> flag. The default value is alpine in our case.
  • The FROM instruction initialises a new build stage and sets the Base Image for subsequent instructions.
  • The RUN instruction will execute any commands in a new layer on top of the current image and commit the results. The resulting committed image will be used for the next step in the Dockerfile. In our case it is a simple Text message denoting build initiation.
  • The ENV instruction sets the environment variable home to the /server. This value will be in the environment for all subsequent instructions in the build stage and can be replaced inline in many as well.
  • The WORKDIR instruction sets the working directory to ${home}for any RUN, CMD, ENTRYPOINT, COPY and ADD instructions that follow it in the Dockerfile.
  • The multiple ADD instructions used copies files, directories or remote file URLs from <src> and adds them to the filesystem of the image at the path <dest>.
  • The RUN instruction used begins building the program binary.
  • The EXPOSE instruction informs Docker that the container listens on the specified network ports at runtime. You can specify whether the port listens on TCP or UDP, and the default is TCP if the protocol is not specified.
  • The final command ENTRYPOINT allows to configure a container that will run as an executable.

Build image

docker build -t samarthya/serviceingo:v1.0 .

Run the image

docker run -d -p 9090:8090 --name smv samarthya/serviceingo:v1.0
REPOSITORY                           TAG                                              IMAGE ID            CREATED             SIZE
samarthya/serviceingo                v1.0                                             10bc4a2e8183        15 hours ago        409MB

docker inspect can elaborate more in the image create.

[
    {
        "Id": "sha256:10bc4a2e8183df14784a0ec97856559e1d8bf8c3f3dded73ece5b74a01da0f46",
        "RepoTags": [
            "samarthya/serviceingo:v1.0"
        ],
        "RepoDigests": [
            "samarthya/serviceingo@sha256:bac7"
        ],
        "Parent": "sha256:ba00",
        "Comment": "",
        "Created": "2020-08-12T14:33:20.916677548Z",
        "Container": "1af",
        "ContainerConfig": {
            "Hostname": "1afe36040e10",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "ExposedPorts": {
                "8090/tcp": {}
            },
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/go/bin:/usr/local/go/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                "GOLANG_VERSION=1.15",
                "GOPATH=/go",
                "home=/server"
            ],
            "Cmd": [
                "/bin/sh",
                "-c",
                "#(nop) ",
                "ENTRYPOINT [\"/server/main\"]"
            ],
            "Image": "sha256:ba0",
            "Volumes": null,
            "WorkingDir": "/server",
            "Entrypoint": [
                "/server/main"
            ],
            "OnBuild": null,
            "Labels": {}
        },
        "DockerVersion": "19.03.12",
        "Author": "",
        "Config": {
            "Hostname": "",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "ExposedPorts": {
                "8090/tcp": {}
            },
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/go/bin:/usr/local/go/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                "GOLANG_VERSION=1.15",
                "GOPATH=/go",
                "home=/server"
            ],
            "Cmd": null,
            "Image": "sha256:ba00f",
            "Volumes": null,
            "WorkingDir": "/server",
            "Entrypoint": [
                "/server/main"
            ],
            "OnBuild": null,
            "Labels": null
        },
        "Architecture": "amd64",
        "Os": "linux",
        "Size": 409358142,
        "VirtualSize": 409358142,
        "GraphDriver": {
            "Data": {
                "LowerDir": "/var/lib/docker/overlay2/ca784789ba90274d9bb7ea66d6fd88bb802f04a81117b33e271fbcf05a52f0ec/diff:/var/lib/docker/overlay2/3148cf2fd8b0c66a0609dfcdf19cad2e6434117379765f4329eca82d750e2b1b/diff:/var/lib/docker/overlay2/6ff4ab6c9f99471ca4d4c06fefdfa80fe95b2eda9505e55d2b2b7746d4a3070d/diff:/var/lib/docker/overlay2/756a454e35cf1dfcf450829ddd10f90a85b8b41e447a01d3a1c483a06b6a6e0d/diff:/var/lib/docker/overlay2/4e64169defbd603b6c390e9e2447a2a1d7596b46a516013e03e43b15d2e1e0fa/diff:/var/lib/docker/overlay2/c0f2ddbe44ea7b5fb17a3074ceae1478c08d0dce890c5d17b25c32b17fe0904a/diff:/var/lib/docker/overlay2/7af1b9667dc01775de4c71554e10e54e3cc424000dd1823f26682065c74fd7e4/diff:/var/lib/docker/overlay2/42c28bbea609cc637ca22830bd78a5a8b9f1f15385d21abd8ddd37bb12917304/diff:/var/lib/docker/overlay2/bb96c77843dbe71872b0b5368519eee56e5f13883c8fd1eb2184724ff93dba70/diff:/var/lib/docker/overlay2/db8152e75c500db9e23be1063f963527a685c61552a12b1c13d23d43af621ef9/diff:/var/lib/docker/overlay2/6f5/diff",
                "MergedDir": "/var/lib/docker/overlay2/c38/merged",
                "UpperDir": "/var/lib/docker/overlay2/c38/diff",
                "WorkDir": "/var/lib/docker/overlay2/c38/work"
            },
            "Name": "overlay2"
        },
        "RootFS": {
            "Type": "layers",
            "Layers": [
                "sha256:506",
                "sha256:0f7",
                "sha256:1ba1",
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                "sha256:23a",
                "sha256:a3e",
                "sha256:4ea8",
                "sha256:ea8c",
                "sha256:dd2"
            ]
        },
        "Metadata": {
            "LastTagTime": "2020-08-12T14:33:20.942126827Z"
        }
    }
]

References