Dockerfile COPY Caveat

Imagine when you have snippet like this:

FROM node:14.19.1-alpine3.15 AS builder
WORKDIR /app
RUN npm run build

That produces static files as seen below:

/app/dist/
├── app.bundle.js
├── fonts
│   └── nerd.ttf
├── index.html
└── static
    └── main.css

And then you want to copy the files into new stage:

FROM alpine:3.15.4 AS runner
COPY --from=builder /app/dist/* /var/lib/nginx/html/

But you get a different file structures:

/var/lib/nginx/html/
├── app.bundle.js
├── index.html
├── main.css
└── nerd.ttf

You may assume (at least I did) there's something wrong with the build command. The COPY instruction doesn't work like cp -R /src/* /dest/ command does in unix shell.

But why??

Workaround

Luckily, a simple modification on the COPY instruction solved the issue.

So, instead of

COPY --from=builder /app/dist/* /var/lib/nginx/html/

do

COPY --from=builder /app/dist/ /var/lib/nginx/html/

The structures are preserved correctly then.

/var/lib/nginx/html/
├── app.bundle.js
├── fonts
│   └── nerd.ttf
├── index.html
└── static
    └── main.css

Moral of the story

• Don't expect the COPY instruction always do the same thing as cp command does.