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Towards A Configuration Specification Language for Internet Systems. Archana Ganapathi ([email protected]). Motivation – Internet Services. Failures impact availability End user satisfaction Economic repercussions Predominant causes Human operator Software.

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motivation internet services
Motivation – Internet Services
  • Failures impact availability
    • End user satisfaction
    • Economic repercussions
  • Predominant causes
    • Human operator
    • Software

[Oppenheimer et al. Architecture, operation, and dependability of large-scale Internet services: three case studies.IEEE Internet Computing special issue on Global Deployment of Data Centers, September/October 2002.]

recap service failure cause
Recap: Service Failure Cause

Online

Content

Total: 61 failures in 12 months

Total: 56 failures in 3 months

[Failure Analysis of Two Internet Services - Winter 2003 ROC Research Group Retreat, Granlibakken, CA, January 2003.]

case study of mis configurations
Case Study of Mis-configurations

~25 problems from Online & Content

  • Errors in component-specific configuration
  • Multi-component configuration inconsistency
  • Non-configuration failure solvable by reconfiguration?
configuration scenarios
Configuration Scenarios
  • Never intended
    • Unacceptable behavior
  • Anticipated and tested
    • Problems with solutions (e.g. recovery code)
  • Anticipated but not tested
    • Rare occurrence, high cost of testing
  • Never anticipated
    • New/evolving environments/interactions
configuration tools
Configuration Tools

Psgconf

Quattor

Radmind

REMBO

Rdist

RPM

Rsync

SmartFrog

SUE

System Imager

SysTracker

Tivoli

Unison

Xhier

Zenworks

Apple Netinstall

BCFG

BCONFIG

BigFix

Cfengine

EDG Fabric Management

Grid Weaver

HP Utility DataCentre

ISconf

Jumpstart/Kickstart

LCFG

Microsoft SMS

Netcool

Novadigm Radia

NPACI Rocks

configuration languages
Configuration Languages:

Windows Registry:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\10.0\Word\InstallRoot]

"Path"="C:\\Program Files\\Microsoft Office\\Office10\\“

Shell Script:

if (! $?YPDOMAIN && -r $LOGHOME/.domainname) then

setenv YPDOMAIN `cat

$LOGHOME/.domainname`

if ("$YPDOMAIN" == "") unsetenv YPDOMAIN

endif

XML:

<server>

<server-name>oski</server-name>

<num-connections>3</num-connections>

</server>

configuration needs
Configuration Needs
  • Account for Human Component
  • Dynamic Monitoring of System Functionality
  • Authenticate Privacy and Integrity
  • Programmatic Manipulation of Configuration Data
  • Domain Independence
configuration needs contd
Configuration Needs contd.
  • User Intent rather than Low Level Assembly Language
  • Intra-Configuration Constraints (Consistency)
  • Inter-Configuration Constraints (Conformity)
  • Formalization and Automatic Derivation
desired language features
Desired Language Features
  • Descriptive:
    • Capture inter- and intra- component interactions
      • User intent and assertions for proper behavior
      • Expressions for failure models & recovery code
      • temporal event relationships
  • Prescriptive:
    • recovery mechanisms for anticipated events
    • “Software TDR”
learning model

Service Requests

Response

System spec

Services spec

Event

logs

Internet System

Configuration

Generator

Error Models

Configuration

Files/Software

Operator modifications

“Learning” Model
lisa framework
LISA Framework
  • Formal models for configurations in IS
    • Recovery handlers
    • Assertions & consistency checking
    • Coverage/utilization
  • Uncover pitfalls in configuration APIs
    • Dependence analysis
    • Conformity checks
  • Use LISA verification modules to authenticate changes
lisa statement structure
LISA Statement Structure

pre_condition ==> rule_body

Pre_conditions = temporal sequences.

Rule_body = action handlers invoked upon matching pattern

Example:

pre-condition:

“A->B: ping” is not followed by

“B->A:‘I’m alive’” within 5 sec

rule body:

A should time out and try C instead.

language features
Language Features

• IS events and transactions

• specify event order and transactions

• temporal sequences with references to past and future

• logic connectives (and, or, not operators)

• repetition, concatenation and overlap of sequences

• sequence vs con-sequence

lisa syntax
LISA syntax
  • LISA_Statement ::= Assertion Action
  • Action ::= ==>{<ok message>, <recovery code>} | ε
  • Assertion ::= assert Property @ ISA_clk ;
  • Property ::= Sequential_Expression | Logical_Expression | Temporal_Operation
lisa operators
LISA Operators

Logical: and(&), or(|), not(~)

Sequential: concatenation(;), overlap(:)

Implication:

-> -- logical if or sequential implication

<-> -- logical iff implication

=> -- temporal ‘next’ implication

Extended Regular Expressions

* -- 0 or more repetition

+ -- 1 or more repetition

? -- optional

[] -- count qualifier

lisa semantics
LISA Semantics

Semantics defined by model represented by triple <A,F,S>.

  • A is a non-empty set of atomic propositions.
  • S is a finite set of states.
  • F is a function that maps each state from S to the alphabet 2A, with a set of valid atomic propositions.

F:S → 2A

f |═ b Boolean expression b holds under truth assignment represented by f

f |═ b <═> b ε f

f |═ ¬b <═> f |≠ b

f |═ b1 & b2 <═> f |═ b1 and f |═ b2

f |═ b1 | b2 <═> f |═ b1 or f |═ b2

examples
Examples
  • If a is True intermittently or continuously for 3 ISA_cycles then after that b must be True within 4 ISA_cycles, unless c happened in the meantime.

assert always (a[1..3]) => b[1..4] | c) @ISA_clk

  • Byzantine fault tolerance, checking if n > 3f always holds [Castro & Liskov]

assert always (up_nodes > 3*const_f)

examples contd
Examples contd.
  • Network property to guarantee “free of routing loops”: at most one entry in table, count less than number of nodes in network.

assert always {(seqa < seqb) - (seqa = seqb ^ hop_a > hop_b)}

  • Perfect failure detector protocol for completely synchronous systems [Fetzer]; to verify the status of a system component c, a configuration process asserts function ISA_f(c) == “up”.

function ISA_f (component c)

{

send ping to c;

wait on receive pong from c return “up”;

after 2*τ return “crashed”;

}

always (on receive ping from sender send pong to sender);

lisa to verilog
LISA to Verilog

IS-dictation:

Within 1 to 3 ISA_cycles after ISA_event ping occurs, ISA_event pong must occur

assert always {~ping; ping} -> {~pong[1..3]; pong} @(ISA_clk)

Verilog program (hand-written; non state-machine model)

always @(ping)

begin

repeat (1) @(ISA_clk);

fork: P

begin @(pong); $display($time,,"Computer up"); disable P;

end

begin repeat (2) @(ISA_clk); $display($time,,"Computer crashed"); disable P;

end

join

end

slide21

Deployment Run-time

Consider ISA_clock = 2*τ

τ ping = 0 pong = 0

3*τ ping = 1 pong = 0

5*τ ping = 0 pong = 1

7*τ ping = 1 pong = 1 *** assertion failure 5*τ ► 7*τ

9*τ ping = 0 pong = 0

11*τ ping = 1 pong = 0

13*τ ping = 0 pong = 1

15*τ ping = 1 pong = 0

17*τ ping = 0 pong = 0

19*τ ping = 0 pong = 0

21*τ ping = 0 pong = 0

23*τ ping = 0 pong = 0 *** assertion failure 13*τ ► 21*τ

lisa future work
LISA Future Work
  • Implement LISA to Verilog compiler
  • Implement Internet Service event monitor with simulated events (anticipatory event sequences)
  • Incorporate dynamic “learning” phase
  • Deploy at actual Internet Service sites.
need data please help
Need Data….Please Help
  • What configuration tasks are regularly performed and why
    • Good/bad “event sequences”
  • Types and impact of configuration failures
  • Desired language features for system configuration
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