Health monitoring in ASP'NET

1
Health monitoring in ASP.NET

• Alex Thissen
• Class-A

Session Code AS.01
2
Agenda

• Instrumenting your application
• ASP.NET tracing
• Web Events
• Events and providers
• Rules and profiles
• Buffering
• Customizing web events
• Other instrumentation options

3
Instrumenting your application

• An instrumented application is able to
• Signal specific events as they occur
• Provide an indication on performance and health
• Without instrumentation you have no clue what
  your application is doing
• Essentially you are looking at a black box
• Add instrumentation to your application from the
  start

4
Options for instrumentation

• .NET instrumentation
• Performance counters
• Application tracing
• ASP.NET 2.0 specific
• Provider based system for Web Events
• Tracing
• Windows OS
• Event tracing for Windows

5
ASP.NET tracing

• Tracing facilities baked into ASP.NET
• Different from .NET tracing
• Trace output is appended at end of page
• Outputs key page lifetime events by default

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ASP.NET tracing configuration

• Specify default settings in web.config file
• Page directive overrules enabled and mode

ltconfigurationgt ltsystem.webgt lttrace
enabled"true" requestLimit"10"
localOnly"true" pageOutput"false"
mostRecent"true" traceMode"SortByTime"
writeToDiagnosticsTrace"false" /gt
lt/system.webgt lt/configurationgt
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Trace configuration details

• Limit number of requests
• requestLimit attribute
• Special section on Trace Information
• Sortable by time or category
• traceMode attribute
• Circular tracing
• Keeps most recent requests
• Specified by mostRecent"true"

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Viewing trace information

• Trace information available through special HTTP
  handler trace.axd
• Control visibility with attributes
• pageOutput appended to end of page (default)
• localOnly available from local machine only
• Redirect to .NET diagnostics
• writeToDiagnosticsTrace attribute of lttracegt

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Adding to trace output

• You can add information only to Trace Information
  section
• TraceContext allows programmatic access
• Inside page with Page.Trace property
• Always via HttpContext.Current.Trace
• Key methods are Write and Warn
• Warn uses red font for emphasis
• Take message and category
• WebPageTraceListener redirects .NET trace info to
  ASP.NET trace

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Reading trace output

• Customize output generated by ASP.NET
• Handle TraceContext.TraceFinished event
• TraceContextRecord contains details
• Optional exception information

protected void Page_Load(object sender, EventArgs
e) this.Trace.TraceFinished new
TraceContextEventHandler(OnTraceFinished) void
OnTraceFinished(object sender, TraceContextEventAr
gs e) ICollection records e.TraceRecords
foreach (TraceContextRecord record in records)

11
Web Events
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Health monitoring events

• Framework for monitoring status of running
  applications and logging significant events
• Health monitoring
• Security auditing
• Runtime observation
• Extensible and provider based model
• Enabled by default
• Configurable settings in Web.config

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Web Events

• ASP.NET comes with several key events
• Request, errors, auditing, heartbeat and
  application lifetime events
• All derive from WebBaseEvent base class
• Event types are mapped in Web.config

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Mapping events

• Web.config contains named events
• Differ by type and event code range
• Base classes can also be mapped
• All available event types are mapped by default
  in machine-level web.config
• Remove existing or add custom events

lteventMappingsgt ltremove name"Infrastructure
Errors" /gt ltadd name"Hack Attempts" type""
startEventCode"0" endEventCode"2147483647"
/gtlt/eventMappingsgt
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Raising web events

• Built-in web events are raised by ASP.NET runtime
• Raise (custom) web events yourself
• Instantiate new event object of desired type
• Make sure event code is offset by 100.000
  (WebEventCodes.WebExtendedBase)
• Call instance or static WebBaseEvent.Raise method
• Rules determine if event actually fires

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Event codes

• Event codes specify reason for raising of a
  particular event
• .NET Framework contains predefined event codes
• Ranges for various types of events
• Offset by base values
• WebEventCodes class has constants for codes and
  offsets

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Rules

• A rule determines
• which event(s) is/are handled
• by which provider
• under what conditions
• To capture similar events use common base class
  event
• E.g. WebBaseErrorEvent for all errors events
• Throttle event raising by specifying minimum
  interval between events

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Defining rules

• By default a rule fires if
• minimum interval is respected
• maximum limit is not exceeded
• Use custom rule for different evaluation

ltrulesgt ltadd name"Failure Audits Default"
eventName"Failure Audits" provider"EventLogProvi
der" minInstances"1" maxLimit"Infinite"
minInterval"000100" custom"" /gt lt/rulesgt
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Custom rules

• A custom rule contains alternate implementation
  of firing logic
• Custom type should implement IWebEventCustomEvalua
  tor
• Single method CanFire determines firing
• Decide based on RuleFiringRecord object
• Time event last fired
• Number of times event was raised before
• Specify custom type in custom attribute

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Profiles

• Named set of parameters for event logging
• Allows for a centralized administration
• Rules can refer to profile names
• Instead of defining parameters inside rule

ltprofilesgt ltadd name"Critical"
minInstances"1" maxLimit"Infinite"
minInterval"000000" custom""
/gt lt/profilesgt ltrulesgt ltadd name"Hack Attempts
Default" profile"Critical" eventName"Hack
Attempts" provider"" /gt lt/rulesgt
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Event providers

• Event providers are actually consumers
• Handle channelling of raised web events
• Available providers can channel to
• .NET diagnostics trace
• Event log
• Windows Management Instrumentation
• SMTP mail recipient
• predefined or templated mail
• SQL Server

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Details of an event

• Providers log details of events
• Certain details are common
• Time, ID, sequence, event code, machine name, app
  path
• Extra details are handled differently per event
  and per provider
• Custom event class should write extra details to
  WebEventFormatter

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Creating custom events

• Derive from appropriate event base class
• Add extra properties for details
• Override FormatCustomEventDetails to output
  details
• Optionally override other methods
• Raise, ToString and IncrementPerfCounters
• Map event in configuration
• Add rules to channel event to provider

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Custom providers

• A custom web event provider ultimately derives
  from WebEventProvider
• Must implement
• Flush usually no logic needed
• ProcessEvent actual handling of event
• Shutdown cleanup of resources
• Decide whether buffering is needed
• Use base class BufferedWebEventProvider
• Do implement Flush method

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Buffering of events

• Buffering queues several events before executing
  specific action
• Prevents flooding by high-volume events
• Conveniently packs multiple events, e.g. mail
• Provider must derive from BufferedWebEventProvider
  
• Out-of-box only SQL Server and mail provider

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Flushing of buffers

• Buffers are flushed
• at regular intervals based on timer
• if urgency threshold is exceeded
• when requested by call to WebEventManager.Flush
  on provider(s)
• Flushes are performed by multiple threads up to a
  certain maximum
• Events are discarded if buffer overflows maximum
  buffer size

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Buffering configuration

• Always set maxFlushSize less than maxBufferSize
• Use maxBufferThreads with caution

lthealthMonitoringgt ltbufferModesgt ltadd
name"Critical Notification" maxBufferSize"100"
maxFlushSize"20" urgentFlushThreshold"1"
regularFlushInterval"Infinite"
urgentFlushInterval"000100" maxBufferThreads"1
" /gt lt/bufferModesgt lt/healthMonitoringgt
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Logging to SQL Server

• Must use mixed mode authentication
• For full SQL Server only
• Cannot use Integrated Security
• By default uses SQL Express instance and
  App_Data\AspNetDB.mdf database
• Prepare database with scripts
• InstallCommon.sql
• InstallWebEventSqlProvider.sql

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Heartbeat

• Check condition of web application with heartbeat
• Raises events of type WebHeartbeatEvent
• Conveys statistics in WebProcessStatistics
• Memory usage
• Number of app domains and threads
• Requests executing, queued and rejected
• Beat interval determined at lthealthMonitoringgt
  element

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More instrumentation options
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.NET tracing

• System.Diagnostics namespace contains
  instrumentation types
• Trace and Debug class allow output to listeners
• Register one or more listeners
• Create custom listeners for other output

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Performance counters

• .NET runtime uses Windows performance counters
  for statistics
• 95 ASP.NET specific counters available
• Counters categorized by FX and application
• .NET runtime itself has counters as well
• Ability to increment counters from managed code

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Event Tracing for Windows

• High performance unified logging system
• One-way packetized I/O
• Managed by kernel
• Characteristics
• Very low overhead
• Uniform way of handling log events
• No managed API prior to .NET 3.5
• Enterprise Instrumentation Framework (EIF) has
  support for ETW

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Review

• Instrumenting your web app can give insights in
  its health and performance
• Several instrumentation options available in
  ASP.NET
• Simple scenarios can use ASP.NET Tracing
• Web events for advanced eventing
• Customizable framework
• Complemented by .NET Framework and OS diagnostics

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Questions

• ?

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