After a brief presentation of configuration management (CM) basics, we start with an ill-fated tale from the recent past about disaster recovery (also known as a case study, if you must): how our CM saved us, how it didn't, and what could have been done better. This could lead to a discussion about best practices.
We use Cfengine 3, and will introduce the software, overview the main differences with other open source CM tools before explaining why we like this choice. But Cfengine is not all: what enables us to manage our configuration completely are the practices and tools we've built around it.
A tale of Disaster Recovery (Cfengine everyday, practices and tools)
1. FOSDEM 2011 @Brussels, Belgium
A tale of disaster recovery
Cfengine everyday, practices and tools
Nicolas Charles <nch@normation.com>
Jonathan Clarke <jcl@normation.com>
2. About the speakers
Nicolas Charles Jonathan Clarke
Cfengine contributor OpenLDAP commiter
Cfengine ”Community
Champion” (C3)
Scala Developer Sysadmin
But we get on pretty well!
(mostly...)
3. Agenda
1) Configuration Management 101
2) Our choice of tool
3) A tale of disaster recovery
4) Introducing Cfengine 3
5) Why we love Cfengine 3
5. Configuration management
What is it ?
Configuration Management is a field of
management that focuses on establishing and
maintaining consistency of a system (..)
throughout its life
Software configuration management is the task
of tracking and controlling changes in the
software
Sources:
http://en.wikipedia.org/wiki/Configuration_management
http://en.wikipedia.org/wiki/Software_configuration_management
6. Configuration management
Why is it useful ?
Control changes
Reproduce over time and nodes
Audit and keep history data
Repair automaticaly
11. Disaster Recovery
An ill-fated tale
from the recent past
(CASE STUDY)
12. Before the disaster...
Our company's IT infrastructure
Small company: small requirements
Web site, email
Git repository, Redmine...
Small company: small budget
All on one hosted server
13. Asking for trouble?
Just one hosted server! Critical services!
No, a ”safe” configuration:
Redundant hardware, 3 disk RAID-5 array
All services automatically installed and setup
using Configuration Management
Backups: daily (several off-site locations)
Several VMs to separate services
14. A critical failure
2 hard drives fail simultaneously
→ RAID-5 array is down
→ Almost all services fail immediately
→ ”The end of the world as we know it”
→ Need to rebuild everything NOW
15. Recovering
Step 1: Panic!
Step 2: Get a new server
Step 3: Reinstall base OS + virtualization
Step 4: Restore VM configuration... whoops
Step 4: Re-create the VMs manually
Step 5: Reinstall each OS in each VM...
16. Recovering
Step 6: Installation Configuration Management
Step 7: Sit back and watch all the services
coming back online as if by magic!
Step 8: Huh, where's my data?
Step 9: Manually restore backups
Step 10: Make a list of missing data...
17. Lessons learned
1) Hard disks fail reliably
2) Restoring virtualization setups:
● Backing up the config files would have helped
● Need CM tools to describe the desired state!
(Cfengine Nova does this)
3) Configuration Management should tie in to our
backup system
4) Backups were lacking some files: always test!
18. Wishlist and discussion
Integrating Configuration Management tools
and backup systems is a crucial step for CM
to be efficient for disaster recovery
What do others do?
Provisioning VMs and their resources (disks,
network) should be automated too
Cloud providers are one solution
What about ”plain” virtualization?
19. A bit about Cfengine 3...
Sources: across the Internet
21. Cfengine 3: Intro
Configuration management software
Written in C
Two versions :
Community (GPL v3)
Nova (closed source) : Community + extra
features
Backed by Cfengine AS – Norway based
company founded in 2009
22. Cfengine 3: Features
According to Kuleven comparative study of
configuration management systems:
Very mature
Cross platform (*BSD, AIX, HP-UX, Linux, Mac
OS X, Solaris, Windows)
Strongly distributed
Based on state description and convergence
Very high scalabily ( > 10000 nodes )
Very small footprint
Source: http://distrinet.cs.kuleuven.be/software/sysconfigtools/overview
23. Cfengine 3: Components
Cf-agent
Runs on all managed hosts
Applies configuration – this is the heart
Can connect to cf-serverd to get policies / files
Cf-serverd
Distributes policies and files
Must be run on policy server(s)
Usually run on all hosts to enable remote runs
Cf-monitord
Collects statistics on all nodes
24. Cfengine 3: Promises
Configuration rules are called promises
”Promise” to be in the desired state
Cfengine agent handles the steps to get there:
convergence
Promise theory is based on research done in
the University of Oslo
25. Cfengine 3: Usage examples
Large companies (Facebook, AMD, …)
Critical systems: Joint Australia Tsunami
Warning Centre
Personal computers
Mobile devices: Nokia N900
Underwater devices: army submarines
Small and medium companies...
26. Why we love Cfengine 3...
Sources: our experience and opinions
28. Multi-platform
Define a configuration for all operating systems
Windows, Linux
Make it ”transparent” (forget about the
complexity)
Existing standard library handling the
differences between each OS and distribution
29. File editing
Only change what you need to
You like your distribution's defaults?
You have various different systems already
setup and just need to change something?
Search for lines and replace/delete/add them
Only change one field in a file
/etc/passwd for example...
30. Complex tasks
Powerful class system to trigger promises
Based on nodes itself
Based on time
Based on whatever you might imagine
Complex workflow can be created
31. Thank you !
FOSDEM 2011
Configuration Management room
And those brave enough to wake up early