I have an app whose only dependency is flask, which runs fine outside docker and binds to the default port
5000. Here is the full source:
from flask import Flask app = Flask(__name__) app.debug = True @app.route("/") def main(): return "hi" if __name__ == "__main__": app.run()
The problem is that when I deploy this in docker, the server is running but is unreachable from outside the container.
Below is my Dockerfile. The image is ubuntu with flask installed. The tar just contains the
index.py listed above;
# Dockerfile FROM dreen/flask MAINTAINER dreen WORKDIR /srv # Get source RUN mkdir -p /srv COPY perfektimprezy.tar.gz /srv/perfektimprezy.tar.gz RUN tar x -f perfektimprezy.tar.gz RUN rm perfektimprezy.tar.gz # Run server EXPOSE 5000 CMD ["python", "index.py"]
Here are the steps I am doing to deploy
$> sudo docker build -t perfektimprezy .
As far as I know the above runs fine, the image has the contents of the tar in
/srv. Now, let"s start the server in a container:
$> sudo docker run -i -p 5000:5000 -d perfektimprezy 1c50b67d45b1a4feade72276394811c8399b1b95692e0914ee72b103ff54c769
Is it actually running?
$> sudo docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 1c50b67d45b1 perfektimprezy:latest "python index.py" 5 seconds ago Up 5 seconds 0.0.0.0:5000->5000/tcp loving_wozniak $> sudo docker logs 1c50b67d45b1 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit) * Restarting with stat
Yep, seems like the flask server is running. Here is where it gets weird. Lets make a request to the server:
$> curl 127.0.0.1:5000 -v * Rebuilt URL to: 127.0.0.1:5000/ * Hostname was NOT found in DNS cache * Trying 127.0.0.1... * Connected to 127.0.0.1 (127.0.0.1) port 5000 (#0) > GET / HTTP/1.1 > User-Agent: curl/7.35.0 > Host: 127.0.0.1:5000 > Accept: */* > * Empty reply from server * Connection #0 to host 127.0.0.1 left intact curl: (52) Empty reply from server
Empty reply... But is the process running?
$> sudo docker top 1c50b67d45b1 UID PID PPID C STIME TTY TIME CMD root 2084 812 0 10:26 ? 00:00:00 python index.py root 2117 2084 0 10:26 ? 00:00:00 /usr/bin/python index.py
Now let"s ssh into the server and check...
$> sudo docker exec -it 1c50b67d45b1 bash [email protected]:/srv# netstat -an Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 127.0.0.1:5000 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:47677 127.0.0.1:5000 TIME_WAIT Active UNIX domain sockets (servers and established) Proto RefCnt Flags Type State I-Node Path [email protected]:/srv# curl -I 127.0.0.1:5000 HTTP/1.0 200 OK Content-Type: text/html; charset=utf-8 Content-Length: 5447 Server: Werkzeug/0.10.4 Python/2.7.6 Date: Tue, 19 May 2015 12:18:14 GMT
It"s fine... But not from the outside.
What am I doing wrong?
The problem is you are only binding to the localhost interface, you should be binding to
0.0.0.0 if you want the container to be accessible from outside. If you change:
if __name__ == "__main__": app.run()
if __name__ == "__main__": app.run(host="0.0.0.0")
It should work.
Note that this will bind to all interfaces on the host, which may in some circumstances be a security risk - see https://stackoverflow.com/a/58138250/4332 for more information on binding to a specific interface.
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