title: /bin/sh: my_custom command not found inside Docker container
body: <p>The context is the following: I need to run <a href="https://www.ffmpeg.org/" rel="nofollow noreferrer">ffmpeg</a> in a AWS Lambda service that is deployed and build using Docker. Since the docker image we use is not debian and does not includes ffmpeg, I created a binary file with the command and added it to the project files. Then, inside the Dockerfile, I create a link to these binary so the command is included in /bin.</p>
  
  <p>This is the Dockerfile:</p>
  
  <pre><code>FROM lambci/lambda:build-nodejs6.10
  
  
  # Create app directory
  WORKDIR /app
  
  # Install app dependencies
  COPY package.json .
  COPY yarn.lock .
  
  #add ffmpeg files
  COPY binaries .binaries
  
  #make link to ffmpeg
  RUN  ln -s /app/.binaries/bin/ffmpeg /bin/ffmpeg
  
  RUN npm install --global yarn
  RUN yarn install
  RUN yarn global add serverless@~1.24.1
  
  # Bundle app source
  COPY . .
  
  EXPOSE 8080
  CMD [ "yarn", "run", "deploy" ]
  </code></pre>
  
  <p>Although this seems to be working in local environment (the command responds when called from console inside docker's image), it does not work when deployed to stage:</p>
  
  <pre><code>/bin/sh: ffmpeg: command not found
  </code></pre>