1. CIT 470: Advanced Network and System Administration
Services
CIT 470: Advanced Network and System Administration

2. CIT 470: Advanced Network and System Administration
Topics
Service Requirements
Open Architecture
Service Design Principles
CIT 470: Advanced Network and System Administration

3. CIT 470: Advanced Network and System Administration
Servers vs Services
A server is a piece of hardware.
A service is the function that is provided by one or more servers.
CIT 470: Advanced Network and System Administration

4. CIT 470: Advanced Network and System Administration
Services
Distinguish structured computing environment from some standalone PCs.
Large orgs linked through shared services to ease communication and optimize resources.
Typical environments have many services
Fundamental: net, DNS, , auth, printing.
Typical: DHCP, backup, directory, file, license.
Services often depend on other services
Almost everything depends on DNS.
CIT 470: Advanced Network and System Administration

5. CIT 470: Advanced Network and System Administration
Providing a Service
A service is more than hardware + software.
A service must be
Reliable.
Scalable.
Monitored.
Maintained.
Supported.
CIT 470: Advanced Network and System Administration

6. CIT 470: Advanced Network and System Administration
Servers and Services
For a service to be reliable, servers should:
Be as simple as possible.
Have minimum software to run service.
Depend on as few other services as possible.
Depend only on services that are at least as reliable as the service running on the server.
Have access restricted to SAs.
Be as few as needed for performance + reliability.
CIT 470: Advanced Network and System Administration

7. Customer Requirements
Customers are the reason for the service.
How do they intend to use it?
What features do they need?
What features would they like to have?
How critical is the service?
What levels of availability and support are needed?
Service Level Agreement (SLA)
Enumerates services.
Defines level of support.
Commits to response times for problem types.
CIT 470: Advanced Network and System Administration

8. Operational Requirements
Essential to designing a reliable service
What services does it depend upon?
What other services will depend upon it?
How does it interoperate with other services?
How can it be integrated with auth/dir services?
How does the service scale?
How can the service be upgraded?
Downtime requirements.
What systems are affected?
CIT 470: Advanced Network and System Administration

9. CIT 470: Advanced Network and System Administration
Open Architecture
Service should be built around open standards
Check IETF RFCs to see if it’s an open protocol.
Example service: SMTP
Example products: exim, postfix, qmail, sendmail.
Open standards don’t require open source.
Allows vendors to make interoperable products.
Avoids vendor lock-in.
Allows vendor competition (cheaper prices for you.)
Decouples client selection from server selection.
Avoids need for protocol gateways.
CIT 470: Advanced Network and System Administration

10. Requests for Comments (RFCs)
Documentation for Internet protocols, technologies, and methodologies.
Standards track RFCs describe Internet standards (TCP, IP, SMTP) and must be approved by IETF.
Experimental RFCs may become standards.
Best Common Practice RFCs describe how to run services or use protocols.
Informational RFCs is a catch-all including proprietary protocols, April Fool’s jokes, etc.
Available from
CIT 470: Advanced Network and System Administration

11. Principles for Designing a Reliable Service
Simplicity
The more features, the more bugs.
Simplicity increases reliability, ease of maintenance.
Vendor Relations
Can be helpful about configuring service.
Let vendors compete for your business.
Stick to vendors who develop for your platform.
CIT 470: Advanced Network and System Administration

12. CIT 470: Advanced Network and System Administration
Machine Independence
Will eventually move service to new host.
Want to avoid having a downtime.
Want to avoid reconfiguring every desktop.
Use generic DNS alias for machine
Mail server has name romero
DNS alias is smtp
Use virtual IP addresses for non-name svcs
Machine has usual IP address:
Virtual: ifconfig eth0:
CIT 470: Advanced Network and System Administration

13. CIT 470: Advanced Network and System Administration
Dedicated Machines
Put each service on its own machine(s).
If a server crashes, only impacts one service.
Easier to debug if only one service running.
Performance tuning easier with one service.
If you can’t afford a new machine, use a VM.
CIT 470: Advanced Network and System Administration

14. CIT 470: Advanced Network and System Administration
Environment
Safe environment
Improves reliability: AC, UPS, physical security.
Data center usually provides faster network too.
Only rely on services provided by data center.
Restricted access
Customers should not need to login to servers.
More logins decrease stability, performance.
Even Windows can be stable w/o user logins.
CIT 470: Advanced Network and System Administration

15. Principles for Designing a Reliable Service
Service components should be tightly coupled.
Other than redundant components.
Share same power source, network.
Reduces service dependencies (single points of failure.)
Centralize management of service
Managed by one set of SAs.
Support for service by single helpdesk.
Document service.
CIT 470: Advanced Network and System Administration

16. CIT 470: Advanced Network and System Administration
Performance
Latency vs throughput
Latency is delay before data received.
Throughput is how much data sent per second.
Performance problems typically affects one.
Increasing the other will not solve your problem.
Remote sites
May have high latency to main site.
Do you need secondary servers at remote sites?
CIT 470: Advanced Network and System Administration

17. CIT 470: Advanced Network and System Administration
Capacity Planning
Estimate capacity from testing.
Test server at 100 qps, 200 qps, until slow.
Identify resources used by each query
RAM
Disk
Network
CPU
Can service be split onto multiple servers?
Can it be done w/o users noticing?
CIT 470: Advanced Network and System Administration

18. Principles for Designing a Reliable Service
Monitoring
Availability, problems, performance.
Auto-alert front line support.
Customers shouldn’t discover problems before SA.
Capacity planning: CPU, mem, disk, network, licenses.
Service Rollout
First impressions are difficult to change.
Be ready for support: docs, trained helpdesk.
Use one, some, many technique.
CIT 470: Advanced Network and System Administration

19. CIT 470: Advanced Network and System Administration
Key Points
Servers vs desktops
Requirements and hardware differences.
Redundancy
Full vs n+k redundancy.
Hot plug vs hot spare.
Services
Requirements: service, server, customer, op.
Machine independence and open architectures.
Performance
Latency vs. throughput.
CIT 470: Advanced Network and System Administration

20. CIT 470: Advanced Network and System Administration
References
Mark Burgess, Principles of System and Network Administration, Wiley, 2000.
Aeleen Frisch, Essential System Administration, 3rd edition, O’Reilly, 2002.
Thomas Limoncelli, Christine Hogan, Strata Chalup, The Practice of System and Network Administration, 2nd ed, Limoncelli and Hogan, Addison-Wesley, 2007.
CIT 470: Advanced Network and System Administration