Tips n Tricks: 02-BUT How the hell do I access the service in Docker

Prologue

For the unininitiated in this gurukul, I have been approached by few intelligent and erterprising Gen-Z developers (thats what I prefer calling those buddies) to teach and initiate them to become experts in Docker also, BUT BUT BUT... NOT in a Fast Track mode but Slow and Steady mode. AND hence dear friends, I would be sticking to One Tip in a Day in this Tips and Tricks series.

Even my Boss (aka Bhole Baba who also takes the Rudra form of Mahakaal at times) has given the diktat to Mohsin (aka Nandi) to stand with a stick if in case I dare to deviate from the plan ??

So here I am, in this series, with the next tip for today

The problem statement

While my buddies completed:

• the installation of installation of Docker/Docker-Desktop
• tried out few commands like "docker run nginx"

The Million Dollar Question came:

How do I access the service running in the docker container

Hmm... Let me give some background / sysadmin concepts:

How does any service expose itself?

Obvisouly, with TCP/UDP ports.

100% Correct! HTTP services listen to TCP/80, MySQL listens to TCP/3306, DNS might listen on UDP/53.

Now if this is clear, the Mongo container running in your local environment would be listening to TCP/27017

But that TCP/27017 port is exposed inside the container and not visible outside locally

Correct. Absolutely correct. And the trick is..

... While starting the container

... Map the port inside with a port of choice outside

docker run -p 8121:80 nginx        

The flag -p does the port-mapping. In the above example, it is mapping the local port 8121/tcp with the port 80/tcp running inside the container.

and because of this mapping, you can now open your favourite browser and fire: http:/127.0.0.1:8121 and you would see the Nginx WELCOME PAGE.

Yeaaa... We have done it. Now go out and try this with different services using different docker images.

Thats it for today. ENJOY ??

#docker #devOps