dockerfile - running netcat inside docker container -

i have created docker images using below dockerfile.

 ubuntu  run apt-get update \   && debian_frontend=noninteractive apt-get install -y \     net-tools \   && apt-get clean \   && rm -rf /var/lib/apt/lists/* run apt-get update \   && debian_frontend=noninteractive apt-get install -y \     netcat \   && apt-get clean \   && rm -rf /var/lib/apt/lists/* expose 1234 entrypoint bin/bash cmd ["nc", "-l", "1234"] 

i created image aboce docker file , run docker container using image running below command.

docker run -d  -i -p 1234:1234 --name daemon  nc-ubuntu nc -l 1234 

in terminal, run below command.

telnet localhost 1234 

i got below output.

$ telnet localhost 1234 trying ::1... connected localhost. escape character '^]'. connection closed foreign host. 

i trying this sample book docker in practice in chapter 2 manning running docker daemon process.

as per author should below result.

$ telnet localhost 1234 trying ::1... connected localhost. escape character '^]'. hello daemon 

any idea why i'm not getting expected output.

that's never going work. there several problems dockerfile.

1

setting entrypoint /bin/bash means docker run ... going start bash. read this question entrypoint , cmd.

2

since you're in non-interactive mode, bash going exit immediately. consider:

host$ docker run nc-ubuntu host$ 

vs:

host$ docker run -it nc-ubuntu root@e3e1a1f4e453:/#  

the latter, because of -it (which allocates tty device, bash requires in interactive mode), gets bash prompt.

3

neither invocation cause container run netcat...and if did, nothing in dockerfile generate hello daemon response you're expecting.

4

the nc command line incorrect. syntax is:

nc -l -p <port> 

so need:

cmd ["nc", "-l", "-p", "1234"] 

5

if want nc provide hello daemon response, need add appropriate -c command nc command line, in:

cmd ["nc", "-l", "-p", "1234", "-c", "echo hello daemon"] 

this makes final dockerfile like:

from ubuntu run apt-get update \   && debian_frontend=noninteractive apt-get install -y \     net-tools \   && apt-get clean \   && rm -rf /var/lib/apt/lists/* run apt-get update \   && debian_frontend=noninteractive apt-get install -y \     netcat \   && apt-get clean \   && rm -rf /var/lib/apt/lists/* expose 1234 cmd ["nc", "-l", "-p", "1234", "-c", "echo hello daemon"] 

and if build that:

docker build -t nc-ubuntu . 

and run that:

docker run -d  -i -p 1234:1234 --name daemon  nc-ubuntu 

i can telnet port 1234 on host , see expected response:

host$ telnet localhost 1234 trying ::1... connected localhost. escape character '^]'. hello daemon connection closed foreign host. 

at point, container have exited because nc exits after accepting single connection (without additional parameters), , docker contain exits when foreground process exits.

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i don't have access book can't tell if problem book or if have made mistake in implementation, suggest there number of online docker tutorials @ least good.