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After RUN ["./run.sh"], a folder produced by run.sh is visible from inside the script but lost once Docker continues.

Expected behaviour:
I would like to have access to the public/ folder, which is generated by the run.sh script.

Dockerfile

 ...
 RUN mkdir -p /opt/site
 WORKDIR /opt/site
 VOLUME /opt/site
 COPY . .

 RUN ["chmod", "+x", "./run.sh"]
 RUN ["./run.sh"]
 RUN pwd
 RUN ls
 RUN ls public

 FROM nginx
 COPY --from=build-stage /opt/site/public /usr/share/nginx/html

Script

 #!/usr/bin/env bash
 rm -rf public/ node_modules/ node_modules/.bin/ package-lock.json yarn.lock
 npm install
 ls
 touch newfile.txt
 npm run build
 ls

ls from inside the run.sh script after build. The public folder is present.

...
Generated public/sw.js, which will precache 6 files, totaling 197705 bytes.
info Done building in 44.842 sec
*ls*
Dockerfile
config
gatsby-config.js
gatsby-node.js
newfile.txt
node_modules
package-lock.json
package.json
postcss.config.js
public
run.sh
src
static
tailwind.css
tailwind.js

ls from inside the Dockerfile. The public folder is missing and trying to interact with it leads to failure.

Removing intermediate container 1692fb171673
 ---> 474d83267ccb
Step 10/14 : RUN pwd
 ---> Running in 7c351b151904
/opt/site
Removing intermediate container 7c351b151904
 ---> bae37da8b513
Step 11/14 : RUN ls
 ---> Running in 384daf575cae
Dockerfile
config
gatsby-config.js
gatsby-node.js
package-lock.json
package.json
postcss.config.js
run.sh
src
static
tailwind.css
tailwind.js
Removing intermediate container 384daf575cae
 ---> 1f6743a4adc1
Step 12/14 : RUN ls public
 ---> Running in 7af84c5d72a0
ls: cannot access public: No such file or directory
The command '/bin/sh -c ls public' returned a non-zero code: 2
ERROR: Job failed: exit code 2

You've created a volume with the selected directory:

 VOLUME /opt/site

When defined in an image, a volume will get created for every container created from that image. If you do not specify a source for the volume (which you cannot at build time), docker will create an anonymous volume. And with both a named and anonymous volume, docker will initialize the contents to that of the image at that location.

The result of a RUN command is the following:

• create a temporary container


• that temporary container runs your requested command and verifies the exit code before continuing


• if successful, docker captures the result of a diff between the image and container. This is mainly the container specific read/write filesystem layer. However it does not include any external volumes.

This behaviour is documented by docker:

• 
  Changing the volume from within the Dockerfile: If any build steps change the data within the volume after it has been declared, those changes will be discarded.

My standard recommendation is to remove any volume definition from the Dockerfile. If you need a volume, define it at runtime with something like a docker compose file. This allows the image to be extended, and prevents anonymous volumes from cluttering the filesystem.