CIT 470: Advanced Network and System Administration. Topics. Servers vs Services. Services

Transcription

1 CIT 470: Advanced Network and System Administration Services CIT 470: Advanced Network and System Administration Slide #1 Topics 1. Service Requirements 2. Open Architecture 3. Service Design Principles CIT 470: Advanced Network and System Administration Slide #2 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 Slide #3 1

2 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 Slide #4 Providing a Service A service is more than hardware + software. A service must be 1. Reliable. 2. Scalable. 3. Monitored. 4. Maintained. 5. Supported. CIT 470: Advanced Network and System Administration Slide #5 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 Slide #6 2

3 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 Slide #7 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 Slide #8 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 Slide #9 3

4 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 Slide #10 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 Slide #11 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 Slide #12 4

5 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 Slide #13 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 Slide #14 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 Slide #15 5

6 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 Slide #16 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 Slide #17 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 Slide #18 6

7 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 Slide #19 References 1. Mark Burgess, Principles of System and Network Administration, Wiley, Aeleen Frisch, Essential System Administration, 3 rd edition, O Reilly, Thomas Limoncelli, Christine Hogan, Strata Chalup, The Practice of System and Network Administration, 2 nd ed, Limoncelli and Hogan, Addison-Wesley, CIT 470: Advanced Network and System Administration Slide #20 7