This document serves as a comprehensive introduction to Docker and container technology, outlining its benefits for developers, operations, and executives. It explains key concepts such as containers, Docker images, deployment techniques, and isolation mechanisms provided by namespaces and cgroups. The document also discusses Docker's evolution, advantages over traditional methods, and its growing community and roadmap for future development.

1. a
Gentle Introduction
to
Docker
and
All Things Containers
December 2013—updated for Docker 0.7

2. Outline
●
Whom is this for?
●
What's the problem?
●
What's a Container?
●
Docker 101
●
Docker images
●
Docker deployment
●
Docker future

3. Outline
●
Whom is this for?
●
What's the problem?
●
What's a Container?
●
Docker 101
●
Docker images
●
Docker deployment
●
Docker future

4. Devs
●
all languages
●
all databases
●
all O/S
●
targetting Linux systems
Docker will eventually be able to target FreeBSD, Solaris, and maybe OS X.

5. Ops
●
any distro
●
any cloud
●
any machine (physical, virtual...)
●
recent kernels
–
at least 3.8
–
or the one that comes with RHEL 6.5

6. CFO, CIO, CTO, ...
●
LESS overhead!
●
MOAR consolidation!
●
MOAR agility!
●
LESS costs!

7. Outline
●
Whom is this for?
●
What's the problem?
●
What's a Container?
●
Docker 101
●
Docker images
●
Docker deployment
●
Docker future

8. The Matrix From Hell
django
web frontend
node.js
async API
background
workers
SQL
database
distributed
DB, big data
message
queue
?
?
?
?
?
?
?
?
?
?
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?
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?
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?
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?
?
?
?
?
?
?
?
?
?
my
laptop
your
laptop
staging
prod on
cloud VM
prod on
bare metal
QA

9. Another Matrix from Hell
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?

10. Solution:
the intermodal shipping container

11. Solved!

12. Solution to the deployment problem:
the Linux container

13. Linux containers...
Units of software delivery (ship it!)
●
run everywhere
–
–
regardless of host distro
–
●
regardless of kernel version
(but container and host architecture must match*)
run anything
–
if it can run on the host, it can run in the container
–
i.e., if it can run on a Linux kernel, it can run
*Unless you emulate CPU with qemu and binfmt

14. Outline
●
Whom is this for?
●
What's the problem?
●
What's a Container?
●
Docker 101
●
Docker images
●
Docker deployment
●
Docker future

15. High level approach:
it's a lightweight VM
●
own process space
●
own network interface
●
can run stuff as root
●
can have its own /sbin/init
(different from the host)
« Machine Container »

16. Low level approach:
it's chroot on steroids
●
can also not have its own /sbin/init
●
container = isolated process(es)
●
share kernel with host
●
no device emulation (neither HVM nor PV)
« Application Container »

17. Separation of concerns:
Dave the Developer
●
inside my container:
–
my code
–
my libraries
–
my package manager
–
my app
–
my data

18. Separation of concerns:
Oscar the Ops guy
●
outside the container:
–
logging
–
remote access
–
network configuration
–
monitoring

19. How does it work?
Isolation with namespaces
●
pid
●
mnt
●
net
●
uts
●
ipc
●
user

20. pid namespace
jpetazzo@tarrasque:~$ ps aux | wc -l
212
jpetazzo@tarrasque:~$ sudo docker run -t
bash
root@ea319b8ac416:/# ps aux
USER
PID %CPU %MEM
VSZ
RSS TTY
STAT
COMMAND
root
1 0.0 0.0 18044 1956 ?
S
root
16 0.0 0.0 15276 1136 ?
R+
aux
(That's 2 processes)
-i ubuntu
START
TIME
02:54
02:55
0:00 bash
0:00 ps

21. mnt namespace
jpetazzo@tarrasque:~$ wc -l
/proc/mounts
32 /proc/mounts
root@ea319b8ac416:/# wc -l
/proc/mounts
10 /proc/mounts

22. net namespace
root@ea319b8ac416:/# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
22: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP>
pfifo_fast state UP qlen 1000
mtu 1500 qdisc
link/ether 2a:d1:4b:7e:bf:b5 brd ff:ff:ff:ff:ff:ff
inet 10.1.1.3/24 brd 10.1.1.255 scope global eth0
valid_lft forever preferred_lft forever
inet6 fe80::28d1:4bff:fe7e:bfb5/64 scope link
valid_lft forever preferred_lft forever

23. uts namespace
jpetazzo@tarrasque:~$ hostname
tarrasque
root@ea319b8ac416:/# hostname
ea319b8ac416

24. ipc namespace
jpetazzo@tarrasque:~$ ipcs
------ Shared Memory Segments -------key
shmid
owner
perms
0x00000000 3178496
jpetazzo
600
0x00000000 557057
jpetazzo
777
0x00000000 3211266
jpetazzo
600
root@ea319b8ac416:/# ipcs
------ Shared Memory Segments -------key
shmid
owner
perms
------ Semaphore Arrays -------key
semid
owner
perms
------ Message Queues -------key
msqid
owner
perms
bytes
393216
2778672
393216
nattch
2
0
2
status
dest
bytes
nattch
status
nsems
used-bytes
messages
dest

25. user namespace
●
●
no « demo » for this one... Yet!
UID 0→1999 in container C1 is mapped to
UID 10000→11999 in host;
UID 0→1999 in container C2 is mapped to
UID 12000→13999 in host; etc.
●
required lots of VFS and FS patches (esp. XFS)
●
what will happen with copy-on-write?
–
double translation at VFS?
–
single root UID on read-only FS?

26. How does it work?
Isolation with cgroups
●
memory
●
cpu
●
blkio
●
devices

27. How does it work?
Isolation with cgroups
●
memory
●
cpu
●
blkio
●
devices

28. memory cgroup
●
keeps track pages used by each group:
–
file (read/write/mmap from block devices; swap)
–
anonymous (stack, heap, anonymous mmap)
–
active (recently accessed)
–
inactive (candidate for eviction)
●
each page is « charged » to a group
●
pages can be shared (e.g. if you use any COW FS)
●
Individual (per-cgroup) limits and out-of-memory killer

29. cpu and cpuset cgroups
●
keep track of user/system CPU time
●
set relative weight per group
●
pin groups to specific CPU(s)
–
Can be used to « reserve » CPUs for some apps
–
This is also relevant for big NUMA systems

30. blkio cgroups
●
keep track IOs for each block device
–
read vs write; sync vs async
●
set relative weights
●
set throttle (limits) for each block device
–
read vs write; bytes/sec vs operations/sec
Note: earlier versions (<3.8) didn't account async correctly.
3.8 is better, but use 3.10 for best results.

31. devices cgroups
●
controls read/write/mknod permissions
●
typically:
–
allow: /dev/{tty,zero,random,null}...
–
deny: everything else
–
maybe: /dev/net/tun, /dev/fuse

32. If you're serious about security,
you also need…
●
capabilities
–
okay: cap_ipc_lock, cap_lease, cap_mknod, cap_net_admin,
cap_net_bind_service, cap_net_raw
–
troublesome: cap_sys_admin (mount!)
●
think twice before granting root
●
grsec is nice
●
seccomp (very specific use cases); seccomp-bpf
●
beware of full-scale kernel exploits!

33. How does it work?
Copy-on-write storage
●
●
●
unioning filesystems
(AUFS, overlayfs)
snapshotting filesystems
(BTRFS, ZFS)
copy-on-write block devices
(thin snapshots with LVM or device-mapper)
Since 0.7, Docker has a storage plugin system!

34. Efficiency

35. Compute efficiency:
almost no overhead
●
●
●
●
processes are isolated,
but run straight on the host
CPU performance
= native performance
memory performance
= a few % shaved off for (optional) accounting
network performance
= small overhead; can be reduced to zero

36. Storage efficiency:
many options!
Union
Filesystems
Snapshotting
Filesystems
Copy-on-write
block devices
Provisioning
Superfast
Supercheap
Fast
Cheap
Fast
Cheap
Changing
small files
Changing
large files
Diffing
Superfast
Supercheap
Fast
Cheap
Fast
Costly
Slow (first time)
Inefficient (copy-up!)
Fast
Cheap
Fast
Cheap
Superfast
Superfast (ZFS)
Kinda meh (BTRFS)
Slow
Memory usage
Efficient
Efficient
Inefficient
(at high densities)
Drawbacks
Random quirks
AUFS not mainline
!AUFS more quirks
ZFS not mainline
BTRFS not as nice
Higher disk usage
Great performance
(except diffing)
Bottom line
Ideal for PAAS and
high density things
This might be the
Future
Dodge Ram 3500

37. Outline
●
Whom is this for?
●
What's the problem?
●
What's a Container?
●
Docker 101
●
Docker images
●
Docker deployment
●
Docker future

39. Docker-what?
●
Open Source engine to commoditize LXC
●
using copy-on-write for quick provisioning
STOP!
HAMMER DEMO TIME.

41. Yes, but...
●
●
●
« I don't need Docker;
I can do all that stuff with LXC tools, rsync,
and some scripts! »
correct on all accounts;
but it's also true for apt, dpkg, rpm, yum, etc.
the whole point is to commoditize,
i.e. make it ridiculously easy to use

42. Containers before Docker

43. Containers after Docker

44. What this really means…
●
instead of writing « very small shell scripts » to
manage containers, write them to do the rest:
–
continuous deployment/integration/testing
–
orchestration
●
= use Docker as a building block
●
re-use other people images (yay ecosystem!)

45. Docker-what?
The Big Picture
●
Open Source engine to commoditize LXC
●
using copy-on-write for quick provisioning
●
allowing to create and share images
●
●
standard format for containers
(stack of layers; 1 layer = tarball+metadata)
standard, reproducible way to easily build
trusted images (Dockerfile, Stackbrew...)

46. Docker-what?
Under The Hood
●
rewrite of dotCloud internal container engine
–
–
●
original version: Python, tied to dotCloud's internal stuff
released version: Go, legacy-free
the Docker daemon runs in the background
–
manages containers, images, and builds
–
HTTP API (over UNIX or TCP socket)
–
embedded CLI talking to the API
●
Open Source (GitHub public repository + issue tracking)
●
user and dev mailing lists
●
FreeNode IRC channels #docker, #docker-dev

47. Outline
●
Whom is this for?
●
What's the problem?
●
What's a Container?
●
Docker 101
●
Docker images
●
Docker deployment
●
Docker future

48. Authoring images
with run/commit
1) docker run ubuntu bash
2) apt-get install this and that
3) docker commit <containerid> <imagename>
4) docker run <imagename> bash
5) git clone git://.../mycode
6) pip install -r requirements.txt
7) docker commit <containerid> <imagename>
8) repeat steps 4-7 as necessary
9) docker tag <imagename> <user/image>
10) docker push <user/image>

49. Authoring images
with a Dockerfile
FROM ubuntu
RUN
RUN
RUN
RUN
RUN
apt-get
apt-get
apt-get
apt-get
apt-get
-y update
install -y
install -y
install -y
install -y
g++
erlang-dev erlang-manpages erlang-base-hipe ...
libmozjs185-dev libicu-dev libtool ...
make wget
RUN wget http://.../apache-couchdb-1.3.1.tar.gz | tar -C /tmp -zxfRUN cd /tmp/apache-couchdb-* && ./configure && make install
RUN printf "[httpd]nport = 8101nbind_address = 0.0.0.0" >
/usr/local/etc/couchdb/local.d/docker.ini
EXPOSE 8101
CMD ["/usr/local/bin/couchdb"]
docker build -t jpetazzo/couchdb .

50. Authoring Images
with Trusted Builds
0) create a GitHub account
On index.docker.io:
1) create a Docker account
2) link it with your GitHub account
3) enable Trusted Builds on any public repo
On your dev env:
4) git add Dockerfile
5) git commit
6) git push

51. Authoring Images
with Chef/Puppet/Ansible/Salt/...
Plan A: « my other VM is a container »
●
write a Dockerfile to install $YOUR_CM
●
start tons of containers
●
run $YOUR_CM in them
Good if you want a mix of containers/VM/metal
But slower to deploy, and uses more resources

52. Authoring Images
with Chef/Puppet/Ansible/Salt/...
Plan B: « the revolution will be containerized »
●
write a Dockerfile to install $YOUR_CM
●
… and run $YOUR_CM as part of build process
●
deploy fully baked images
Faster to deploy
Easier to rollback

53. Outline
●
Whom is this for?
●
What's the problem?
●
What's a Container?
●
Docker 101
●
Docker images
●
Docker deployment
●
Docker future

54. Running containers
SSH to Docker host and manual pull+run
● REST API (feel free to add SSL certs, OAUth...)
● maestro, maestro-ng
(https://github.com/signalfuse/maestro-ng)
● OpenStack Nova
● OpenStack Heat
● who's next? OpenShift, CloudFoundry?
● multiple Open Source PAAS built on Docker
●

55. Orchestration & Service Discovery
●
you can name your containers
●
they get a generated name by default
–
–
●
0.6: red_ant, gold_monkey...
0.7: angry_linus, naughty_tesla...
you can link your containers
docker run -d -name frontdb mysqlimage
docker run -d -link frontdb:sql nginximage
→ container frontweb gets one bazillion environment vars

56. Orchestration & Service
Discovery roadmap
●
●
●
currently single-host
problem:
how do I link with containers on other hosts?
solution:
ambassador pattern!
–
app container runs in its happy place
–
other things (Docker, containers...) plumb it

57. Orchestration roadmap
●
●
●
currently static
problem: what if I want to…
move a container?
do a master/slave failover?
WebScale my MangoDB cluster?
solution:
dynamic discovery!

58. Multi-host Docker deployments
I could give a full talk
about this topic
(and actually I did once)

59. Outline
●
Whom is this for?
●
What's the problem?
●
What's a Container?
●
Docker 101
●
Docker images
●
Docker deployment
●
Docker future

60. Docker: the community
●
Docker: >240 contributors
●
Docker inc.: <20 engineers
●
latest milestone (0.7): >100 contributors
●
~50% of all commits by external contributors
●
GitHub repository: >1000 forks
...and counting!

61. Docker long-term roadmap
Docker 1.0:
●
remove AUFS, THINP, LXC, etc.
–
–
●
storage? cp!
–
●
execution? chroot!
we can run everywhere o/
re-add everything as plugins
discover and interconnect hosts and services
through docker.io

62. Thank you! Questions?
http://docker.io/
http://docker.com/
https://github.com/dotcloud/docker
@docker
@jpetazzo