Docker notes 2022

docker hub 的 IMAGE LAYERS 資訊好像沒啥用處

• Dockerfile source: https://github.com/dockersamples/linux_tweet_app/blob/master/Dockerfile

FROM nginx:latest

COPY index.html /usr/share/nginx/html
COPY linux.png /usr/share/nginx/html

EXPOSE 80 443   

CMD ["nginx", "-g", "daemon off;"]

• published info: https://hub.docker.com/layers/86236225/howtomakeaturn/linux_tweet_app/1.0/images/sha256-fb6f23f1db29c83a80663813deef95e7d086689b2fd85fa800646d1f35fe248c?context=repo

連 FROM 都沒有，想看 base image 都沒辦法欸

有辦法在 docker hub 看到 Dockerfile 嗎

• https://stackoverflow.com/questions/43309737/how-can-i-see-dockerfile-for-each-docker-image

As far as I know, no, you can't. Because a Dockerfile is used for building the image, it is not packed with the image itself.

那 Docker hub 的 image layers 是有什麼用？

• https://stackoverflow.com/questions/63823884/docker-image-layer-what-does-add-filesome-hash-in-mean

That Docker Hub history view doesn't show the actual Dockerfile; instead, it shows content essentially extracted from the docker history of the image. That doesn't preserve the specific details you're looking for: it doesn't remember the names of base images, or the build-context file names of things that get ADDed or COPYed in.

Conclusions

• 有點像是 composer.json vs composer.lock 以及 package.json vs package-lock.json
• 一個是給開發者看的，一個是給機器看的（也不是，畢竟都在網頁上給人看了，應該說是剝開一層抽象啦）
• 難道說，FROM 就是很無腦的把 base image 的一串 Docker 指令 copy & paste 過來？
• 反正，到最後，本來就是一整串 linux commands 到處貼來貼去吧

More

• 想想也是，畢竟 image 是可以用 bash 在裡面改來改去，然後再進行 commit 的
• 這種行為，就不是從 Dockerfile 出發，不是以 Dockerfile 為 single source of truth 了
• https://stackoverflow.com/questions/21548364/after-pulling-a-docker-from-the-repository-how-to-change-the-images-files
• 不過，應該不建議這樣做，設定檔與需要修改的東西，應該用 volume 機制放在 image 外部