Transcript Introduction

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
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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, email, 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
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Reliable.
Scalable.
Monitored.
Maintained.
Supported.
CIT 470: Advanced Network and System Administration
Slide #5
Servers and Services
For a service to be reliable, servers should:
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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
Customer Requirements
Customers are the reason for the service.
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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
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Operational Requirements
Essential to designing a reliable service
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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
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Open Architecture
Service should be built around open standards
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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.
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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
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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 http://www.rfc-editor.org/
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
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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: 192.168.1.54
– Virtual: ifconfig eth0:0 192.168.1.5
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Dedicated Machines
Put each service on its own machine(s).
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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.
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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.
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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
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Performance
Latency vs throughput
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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?
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Capacity Planning
Estimate capacity from testing.
– Test server at 100 qps, 200 qps, until slow.
– Identify resources used by each query
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RAM
Disk
Network
CPU
Can service be split onto multiple servers?
– Can it be done w/o users noticing?
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Principles for Designing a Reliable Service
Monitoring
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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.
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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, 2000.
2. Aeleen Frisch, Essential System Administration,
3rd edition, O’Reilly, 2002.
3. 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
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