This document discusses how DevTable uses Docker containers to securely run development tools and services for users. Some key points: - DevTable runs each user's code in a separate Docker container to isolate potentially dangerous tools like debuggers or terminals. - It uses the Python Docker API and runs an SSH "command and control" process to execute commands inside containers quickly and securely. - When files change, notifications are passed between the backend and container server to keep the container and hosted code in sync. - Dynamic port mapping through HAProxy allows container services to be accessed publicly through subdomains while maintaining isolation. - Docker provides a major speed improvement over their previous LXC solution, booting containers in

1. Docker at DevTable

2. What is DevTable?
DevTable is a browser-based, hosted,
collaborative IDE
Develop in the cloud with the same power as
your desktop applications

3. Code

4. Collaborate

5. Debug and Test

6. Deploy
● Google App Engine
● REST
● SCP
● Git (Heroku and other providers)

7. Sealed evil in a can
There are a lot of neat things that we run for
our users, but they are all potentially very
dangerous:
● App Engine Development Server
● Debuggers and Emulators
● REPLs (Python, etc)
● Terminal support (which means all of the
above as well)

8. Why this is a problem
● Without a containment system of some kind,
any of these awesome features would allow
users to cause mayhem:
○ A REPL use could open any file
○ A DevServer can execute arbitrary code
○ A terminal could allow anything to happen

9. Why not simply use permissions?
● Permissions solve the file access problem
● Permissions do not prevent users from
causing other system issues: instability,
exhaustion, escalation, etc

10. Solution: containers!
To contain the insecurity of running live code,
we run all non-custom code in a container,
with only the user’s project mounted and
available
Evil (not to scale)
Project data
Container

11. Ideal container properties
● Lightweight
● Secure
● Easy to manage
● FAST

12. Originally we used LXC...
● Lightweight (sort of…)
● Secure
● Easy to manage (sort of...)
● FAST

13. In the beginning, there was LXC...
… and it was slow.
● Typical startup times for our containers were
on the order of minutes
● Starting a debugger or shell is not fun at
those speeds
● Getting the security and management just
right was quite painful

14. Then the community said “let there
be Docker”...
Yo!

15. … and it made things amazing.
Our average startup time for a container has
dropped from over a minute to just under
four seconds.
LXC
Docker
Go make a cup of coffee and play swords on office chairs
Go!

16. Before Docker

17. But, but Docker is just... LXC...
Almost, Docker does some things that make
starting up single processes lightning quick:
● Incremental by default
● Replace distro init process with lightweight
version
● No DHCP, upstart, dnsmasq, etc.
● Aufs seems to be faster than OverlayFS
● Build process is MUCH better (Dockerfiles)

18. Docker at DevTable
The fun technical details!

19. DevTable overview
Clients
Web
browsers
Clients -
Web
browsers
Frontends
Python
Clients -
Web
browsers
Backends
C#
WebSocket Socket
DFS
Clients -
Web
browsers
Container
Servers
Python
Thrift
SSH
HTTP
?
Images

20. Things we’ll discuss today
Clients
Web
browsers
Clients -
Web
browsers
Frontends
Python
Clients -
Web
browsers
Backends
C#
WebSocket Socket
DFS
Clients -
Web
browsers
Container
Servers
Python
Thrift
HTTP
SSH
?
Images

21. How we use docker now
● Python Docker API bindings
● Run a single instance per project
● Mount only the files relevant to the project in
the container
● Run an SSH “command and control” process
● Execute user processes through SSH
● Dynamic version of Docker port forwarding

22. Backend <-> Container server
Backends
C#
Container
Servers
Python
Thrift

23. Container server
The container server is the server in charge of
managing all aspects related to the Docker
containers
● Written in Python
● Conforms to a Thrift interface
● Called by the Backends to start containers,
stop containers, run commands, mount file
systems in containers, etc

24. Container server
startContainer
Starts a new container for a project.
runCommand
Runs a command inside a container
stopCommand
Stops a command inside a container
notifyFilesModifed
Notifies a container that a file has been modified by the backend
stopContainer
Stops a container

25. Handling file changes
● Changes made by the container or the
backend to the DFS are propagated
automatically
● However, both sides have code that
depends on notification of changes
● Each server notifies the other about
changes that occur via a notification service

26. DFS change notifications
Backend
C#
Container
Server
Python
Hey, a user added file “test.txt” in container 1234
Backend
C#
Container
Server
Python
Hey, the user changed file “foo.py” in container 1

27. How we handle file changes in
Docker
● The container server watches changes
inside the container using inotify, and
reports changes to the backend
● The backend reports changes to the
container server which will touch files that
have been added or changed

28. Container server <-> Docker
Clients -
Web
browsers
Container
Servers
Python
SSH

29. Container server <-> Docker
We use the Python Docker bindings to create a
new image and load it with a temporary ssh
key
New container requests bring up the container
with the known session SSH key and issue
commands to the container via SSH
Much better than LXC issuing commands via
subprocess

30. Docker <-> Outside world
For many services we run (such as the App
Engine Development Server), we need to
expose the server running inside Docker to
the outside world

31. Docker <-> Outside world
HTTP
Clients
Web
browsers
HTTP
Container Server
HAProxy

32. Docker <-> Outside world
Services inside of Docker as exposed via
dynamic port mapping to a HAProxy
running on the container server
The HAProxy exposes the port by remapping it
to the external port and a custom
subdomain

33. Docker <-> Outside world
Container Server
93nx83ndsc34mn.c4.devtable.io:80Clients
Web
browsers
Port 38563
HAProxy

34. Example: running a dev server
1. Backend requests a container from the
server
Backend
C#
Container
Server
Python
I need a container for project “testapplication”
Container “container1234” started for project

35. Example: running a dev server
2. Backend registers for file notification events
Backend
C#
Container
Server
Python
Let me know if any files change
Duly noted

36. Example: running a dev server
3. Backend asks for the dev server to be
started and port 80 to be forwarded
Backend
C#
Container
Server
Python
Please start the dev server and forward port 80
Dev server started and port is forwarded at
subdomain foobarbaz

37. Example: running a dev server
1. Container server tells Docker to start a
container
Container
Server
Python
create_container, mount_filesystem,
forward_port, start_ssh
Done. Port exposed: 84639

38. Example: running a dev server
2. Container server tells HAProxy to forward
the port returned by docker
Container
Server
Python
Forward port 84639 as subdomain
foobarbaz
HAProxy

39. Example: running a dev server
3. Container server tells Docker to run the dev
server
Container
Server
Python
ssh command_for_devserver

40. Summary
Docker has allowed DevTable to run amazing
tools securely and fast, without a large
management overhead

41. Future opportunities
Docker presents some amazing new
opportunities for DevTable and the
community:
● Ability to quickly load (and save) complete
development environments, securely
● Ability to quickly write custom plugins and
run them in our IDE (want to analyze and
build Go? just give us a URL or a
Dockerfile!)

42. But wait…
There’s something that has been
bugging us…
How should we distribute our
private images in production?

43. Quay Demo
At this point in the live talk we unveiled and
gave a demo of our hosted private docker
registry called Quay.io.

44. Questions? Comments? Witty
anecdotes?
devtable.com
Jacob Moshenko - jake@devtable.com
Joseph Schorr - jschorr@devtable.com