Cannot install package using docker compose

Question

My web app uses Node.js and MongoDB. I am pulling mongo image from docker image hub . When I build an image of my node app it runs fine alone. However when I start up containers using compose it gives the following error. Isn't it supposed to install the packages when image is built from Dockerfile?

web_1 | module.js:457 web_1 | throw err;

web_1 | ^

web_1 |

web_1 | Error: Cannot find module 'mongoose'

web_1 | at Function.Module._resolveFilename (module.js:455:15)

web_1 | at Function.Module._load (module.js:403:25)

web_1 | at Module.require (module.js:483:17)

web_1 | at require (internal/module.js:20:19)

web_1 | at Object. (/worklog/worklog.js:7:14)

web_1 | at Module._compile (module.js:556:32)

web_1 | at Object.Module._extensions..js (module.js:565:10)

web_1 | at Module.load (module.js:473:32)

web_1 | at tryModuleLoad (module.js:432:12)

web_1 | at Function.Module._load (module.js:424:3)

Dockerfile

FROM node

RUN mkdir -p /worklog

WORKDIR  /worklog

RUN npm install mongoose \
    express \
    body-parser \
    express-session \
    method-override \ 
    connect-mongo \
    mongodb

COPY login.html worklog.html workloglist.html worklog.js /worklog/

ENV NODE_VERSION 6.3.1

EXPOSE 4000

CMD npm, start 

docker-compose.yml

db:
  image: mongo
  ports:
    - "27017:27017"
  command: "--smallfiles --logpath=/dev/null"
web:
  build: .
  command: node worklog.js
  volumes:
    - .:/worklog
  ports:
    - "4000:4000"
  links:
    - db
  environment:
    PORT: 4000

Answer 1

The volumes

volumes:
  - .:/worklog

is basically masking everything you installed to /worklog in the build with the files on the host, including /worklog/node_modules if any. You could try

volumes:
  - .:/worklog
  - /worklog/node_modules

which I think overlays the /worklog/node_modules from the container on top of the directory mounted from the host again making the node_modules visible to the app.