Using the following Dockerfile:
FROM alpine:latest
WORKDIR /usr/src/app
COPY ["somefile", "/"]
and the build following command:
docker build \
--file=Dockerfile \
--no-cache=true \
--progress=plain \
--tag=someimage:sometag \
.
=>
#1 [internal] load build definition from Dockerfile
. . .
#8 naming to docker.io/someimage:sometag done
#8 DONE 0.0s
why is somefile found at the root (/):
docker run someimage:sometag ls -altr ../../../.
#=>
total 68
. . .
-rw-r--r-- 1 root root 128 Jul 27 12:34 somefile
. . .
drwxr-xr-x 1 root root 4096 Jul 27 12:34 ..
drwxr-xr-x 1 root root 4096 Jul 27 12:34 .
and not the working directory (/usr/src/app):
docker run someimage:sometag ls -altr .
#=>
total 8
drwxr-xr-x 3 root root 4096 Jul 27 12:34 ..
drwxr-xr-x 2 root root 4096 Jul 27 12:34 .
The COPY instruction in your Dockerfile:
. . .
COPY ["somefile", "/"]
. . .
uses an absolute path instead of a relative path; more on that here.
Replacing / with ./ will COPY somefile to /usr/src/app instead of the root dir:
FROM alpine:latest
WORKDIR /usr/src/app
COPY ["somefile", "./"]
We can locate somefile after we build the image with:
docker run someimage:anothertag ls -altr .
#=>
total 16
-rw-r--r-- 1 root root 128 Jul 27 23:45 somefile
drwxr-xr-x 1 root root 4096 Jul 27 23:45 ..
drwxr-xr-x 1 root root 4096 Jul 27 23:45 .