title: Docker container build faild: "exec: \"flask\": executable file not found in $PATH": unknown
body: <p>I'm learning docker. I try run a sample dockerfile on docker,com. But I have a problem is "Error response from daemon: OCI runtime create failed: container_linux.go:345: starting container process caused "exec: \"flask\": executable file not found in $PATH": unknown
  ".</p>
  
  <pre><code>FROM python:3.7-alpine
  
  WORKDIR /code
  ENV FLASK_APP app.py
  ENV FLASK_RUN_HOST 0.0.0.0
  RUN apk add --no-cache gcc musl-dev linux-headers
  COPY requirements.txt requirements.txt
  RUN pip install -r requirements.txt
  COPY . .
  CMD ["flask","run"]
  </code></pre>
  
  <p>Many thanks. </p>