Docker build does not use cache from npm ci

I have created my Dockerfile with attention to use the docker cache system. I'm adding the package.json and package-lock.json files into a clean container, and then run npm ci command. I expect it to be used from the cache if the package.json and package-lock.json were not changed, but it keeps running. Am I missing something? Is there something wrong with my Dockerfile?

FROM node:13.10.1-stretch as base

ADD package.json /app/package.json
ADD package-lock.json /app/package-lock.json
WORKDIR /app

RUN npm ci --unsafe-perm

The output I get:

Step 1/12 : FROM node:13.10.1-stretch as base
  ---> 7aef30ae6655
 Step 2/12 : ADD package.json /app/package.json
  ---> ce655a3453f2
 Step 3/12 : ADD package-lock.json /app/package-lock.json
  ---> 797cda1e10b2
 Step 4/12 : WORKDIR /app
 Removing intermediate container 5b6929b80ad6
  ---> 80c2aac903c5
 Step 5/12 : RUN npm ci --unsafe-perm
  ---> Running in 7732a8aca146
 > fsevents@1.2.12 install /app/node_modules/webpack-dev-server/node_modules/fsevents
 > node-gyp rebuild
 make: Entering directory '/app/node_modules/webpack-dev-server/node_modules/fsevents/build'
   SOLINK_MODULE(target) Release/obj.target/.node
   COPY Release/.node
 make: Leaving directory '/app/node_modules/webpack-dev-server/node_modules/fsevents/build'
[...]

Solution

Assuming that you don't run other commands before package.json was added, your Dockerfile is fine and the layer adding your package file is cached. For example, we build a simple Dockerfile that just adds your package.json config file:

FROM node:13.10.1-stretch as base
ADD package.json /app/package.json

First run:

$ docker build -t so-example .
Sending build context to Docker daemon  3.072kB
Step 1/2 : FROM node:13.10.1-stretch as base
13.10.1-stretch: Pulling from library/node
[...]
Status: Downloaded newer image for node:13.10.1-stretch
 ---> 7aef30ae6655
Step 2/2 : ADD package.json /app/package.json
 ---> a7bb80c06ecb
Successfully built a7bb80c06ecb
Successfully tagged so-example:latest

Second run

$ docker build -t so-example .
Sending build context to Docker daemon  3.072kB
Step 1/2 : FROM node:13.10.1-stretch as base
 ---> 7aef30ae6655
Step 2/2 : ADD package.json /app/package.json
 ---> Using cache
 ---> a7bb80c06ecb
Successfully built a7bb80c06ecb
Successfully tagged so-example:latest

As you can see, the caching works. Could you please verify this with such a minium example? Most of the time caching breaks because of a suboptimal ordner. Please check the following:

Execute the build command twice. Caching could only work after the first run
Make sure, that no other steps you may havent posted here were executed in your Dockerfile that invalidates the cache
Are there any cleanup commands running? Something like docker prune or docker image prune (or manual list/delete images on older versions) would delete your image
Check/post your calls how you build the image