Understanding containers (part 02): inside a container
Thank for all the feedback after the part 01 of this series. I hope you enjoyed as well some exercises with OrientDB database.
Let’s keep digging into containers!
I assume that you have the container
myorientdb01 running, e.g. by running it with
docker start myorientdb01, if it was stopped in the meantime.
How do I get “into the container”?
I do not know about you, but for me it was the very first question. Used to usual VMs (virtual machines) I was expecting some way to get “inside the container” to work with it.
Quick web search and I found that command to do it, like
docker exec -it myorientdb01 bash
Again, I do not know about you, but for me it was another “Say whaaat??!” moment. “It is not connecting to the container. It is executing a container and calling its OS shell?? And why is IT (as I looked at
But let me calm down and try to understand what’s going on.
The above command is the short version of
docker container exec --tty --interactive myorientdb01 bash,
so basically it tells docker to execute the
bash command inside the running container
Ok, let’s execute that command.
Well, where are we?
Let’s look around what we’ve got here…
…by running a few commands, like
tty and finally
exit (or you can press
Ctrl+D to exit).
Let’s quickly play with these options. First by running the command without
docker exec -t myorientdb01 bash
…and typing something like
exit or even
What am I doing here?.
Even though we connected to terminal in the container, the input from my keyboard is not sent to the terminal. Obviously
Ctrl+D will not work to exit, so I needed
Ctrl+C to interrupt.
Now, let’s try executing
docker exec -i myorientdb01 bash
…and typing commands
This time commands are received by the container and results are displayed, but there is no terminal assigned (as indicated by
not a tty response from the
tty command) and no shell prompt.
Even though I used it to “connect” to the running container, in fact I was just executing
bash command in that running container. That gave me that perception of “being in the container”.
But it means I can use
exec to execute any command from a container without going “into” the container, like…
docker exec myorientdb01 whoami
docker exec --user nobody myorientdb01 whoami
…to see the results. No input or terminal connections were required to execute this commands in the container and get results.
Running client software
So far we tried some basic OS commands in the container that runs the OrientDB server. We used to connect to that server using its web-based Studio via exposed port.
But what if I want to connect to that database using its console client (because I am cool, because I am techie, because I am command line guy, because I try to look geeky, whatever…)?
No need to install that client software, because it is already available in the container in database’s
bin directory, so we can call it using docker, like…
docker exec -it myorientdb01 bin/console.sh "create database remote:localhost/mydb root root"
… to create our own
mydb database using so-called batch mode of the console.
Now I can open Studio and see that database there…
…to which I can connect using standard user
admin with its default password
Ok, my train is arriving…
…to Kraków. Literally. I will be presenting this topic at the “Career in IT” conference tomorrow. And I won’t have time to work on this more tonight, because tonight we have the first ever local SAP Stammtisch in Kraków, organized by Izabela Rębisz. Na zdrowie ?
If you are interested in this topic, but it is too late for you to arrive to Kraków, then I will have the same presentation at SAP Inside Track in Walldorf next month. See you there?
We will keep digging into Docker and containers in next posts. I will tag these posts UnderstandContainers for easy search.
-Vitaliy (aka @Sygyzmundovych)
PS. This was my blog post #100 (decimal, not binary ;-)) on SAP Community ?
Thanks! Nice example of docker exec to run the client within the container. I'd also never experimented with -it parameters, so learned a few things here.
Hi Douglas. Some more — but slightly different — examples in today’s post: Understanding containers (part 03): one-shot containers. Looking forward to your thoughts and experience.