# Presentation: 013087

## Reflections on Reliability Issues in OGSA 

- Matti Hiltunen
- AT&T Labs - Research
- Florham Park, NJ, USA
*hiltunen@research.att.com*

- Disclaimer: This presentation does not reflect the views of AT&T.

## Business Requirements for Grid Computing

- Grid applications:
- “Traditional” batch applications (HPC)
- Interactive applications
- Existing COTS components:
- JVMs, web servers, application servers, etc
- Virtual machines
- Application specific requirements:
- E.g., very high availability required for customer facing applications (e-commerce).
- Cost: $/minute of unavailability

## Current approach (before grid)

- Each business service/application implemented on its own silo of designated resources.
- Typically, no single point of failure.
- Constructing highly available services is expensive!
- Different services fail independently from one another

- Router

- Router

- Firewall

- Firewall

- Loadbalancer

- Loadbalancer

- Web server

- Web server

## Cheaper or Faster (from Globus Alliance)

**Notes:**
TCO = Total Cost of Owneship

## Future approach (with grid)

- OGSA

- Different business services/applications share (some) resources.
- All applications depend on OGSA being reliable (otherwise, shared resources are unavailable).
- Different applications no more quite as independent (compete for same resources).

**Notes:**
TCO = Total Cost of Owneship

## OGSA: A complicated architecture

- LOTS of different services:
- Job Manager, Execution Planning Service, Candidate Set Generator, Reservation, Deployment and Configuration, Security, Information, Naming Services, ...
- To start the execution of an application on a grid, half a dozen (or more) services may need to interact.
- Possible failures:
- Server (hardware or OS) running the service crashes:
- More servers => more failures
- More services on one server => one service may affect another (e.g., memory leaks)
- Service fails (software bug):
- more services => more code => more bugs
- each service smaller => more manageable => hopefully fewer bugs
- Service interaction failures:
- More services => more possibilities for interaction failures.
- Current commercial grid solutions are much simpler!

## OGSA: “Architecture where the failure of a service you have never heard of prevents you from running your  applications?”

- OGSA: “Architecture where an unknown failure of unknown service prevents you from running your applications?”

## What can standards do?

- Not very much:
- standards define interfaces and protocols
- reliability of OGSA services is more of an implementation issue.
- reliability may provide differentiation between different standards compliant implementations.
- What can be standardized for each OGSA service:
- error messages and processing of error messages. (A invokes B which invokes C, C fails, what kind of error message will A get.)
- protocols that completely handle error cases (any partner may fail at any time of the protocol execution or timeouts may occur).
- rich monitoring interfaces.
- tracking interfaces: APIs for submitting test requests that will be tracked through the OGSA architecture.
- Fault tolerance related services:
- Monitoring Service, replications checkpointing, etc
- Help with fault tolerance of jobs, but not the fault tolerance of OGSA services themselves.

## Suggestions (Implementation)

- Fast failure detection and recovery mechanisms.
- End-to-end monitoring (submit test jobs).
- Combine or co-locate OGSA services on same fault-tolerant servers to reduce cost of fault tolerance.
- Hardware fault tolerance, OS-level transparent replication, service-level replication.
- Highly replicated service implementation (P2P style).
- Failure aware service: do not give up too easily (e.g., locate alternate service provider).
- Planned graceful degradation path.

## Conclusions

- Reliability is a MUST for enterprise use of grid computing.
- Complexity of OGSA is scary from reliability point of view.
- Standards have limited role with reliability of OGSA services.
- Implementations and/or deployments of OGSA services must be highly available.