HTTP Request from Dockerfile not successful - docker

Question

I'm playing around with Docker and am trying to get a Dockerfile working running ubuntu and nginx.
The result from "docker build" is that curl is unable to do a HTTP request at localhost, however if I later start the container created from the Dockerfile it works just fine..
What could possibly be the issue here?
See the Dockerfile below:
$ cat Dockerfile
FROM ubuntu:14.10
RUN apt-get update
RUN apt-get install -y curl nginx
RUN service nginx start
RUN echo "niklas9 was here" > /usr/share/nginx/html/index.html
RUN /usr/bin/curl -v "http://localhost/"
Result from "docker build":
$ sudo docker.io build .
...
Step 5 : RUN /usr/bin/curl -v "http://localhost/"
---> Running in 46f773be22a2
* Hostname was NOT found in DNS cache
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0* Trying ::1...
* connect to ::1 port 80 failed: Connection refused
* Trying 127.0.0.1...
* connect to 127.0.0.1 port 80 failed: Connection refused
* Failed to connect to localhost port 80: Connection refused
* Closing connection 0
curl: (7) Failed to connect to localhost port 80: Connection refused
2014/11/26 22:47:38 The command [/bin/sh -c /usr/bin/curl -v "http://localhost/"] returned a non-zero code: 7
Results from starting the container and attaching into it:
root#65c55d5974cb:/# curl -v "http://localhost/"
* Hostname was NOT found in DNS cache
* Trying ::1...
* Connected to localhost (::1) port 80 (#0)
> GET / HTTP/1.1
> User-Agent: curl/7.37.1
> Host: localhost
> Accept: */*
>
< HTTP/1.1 200 OK
* Server nginx/1.6.2 (Ubuntu) is not blacklisted
< Server: nginx/1.6.2 (Ubuntu)
< Date: Wed, 26 Nov 2014 21:50:16 GMT
< Content-Type: text/html
< Content-Length: 17
< Last-Modified: Wed, 26 Nov 2014 21:38:11 GMT
< Connection: keep-alive
< ETag: "54764843-11"
< Accept-Ranges: bytes
<
niklas9 was here
* Connection #0 to host localhost left intact
I'm running Ubuntu 14 with docker installed with apt-get, see version below.
$ docker.io --version
Docker version 0.9.1, build 3600720

Answer 1

Fundamentally, you should not be thinking of firing up your service at build time.
Dockerfile RUN commands are intended to create some state for the final container you are trying to make. Each command creates a new container layer, based on the one before, and Docker caches them to speed things up, so any given RUN command may not actually run at all for a build, unless the things that go before it have changed.
Some notes from Docker on how this works

Answer 2

After the line
RUN service nginx start
is executed, only the changes in the file system are persistent.
The nginx process isn't available when the next line of the dockerfile is executed.
It would work like that, but if you want the nginx process to be started in the container, you would need to add a CMD at the end.
FROM ubuntu:14.10
RUN apt-get update
RUN apt-get install -y curl nginx
RUN echo "niklas9 was here" > /usr/share/nginx/html/index.html
RUN service nginx start && /usr/bin/curl -v "http://localhost/"