distributing transactions using masstransit

Distributing TransactionsChris PattersonFellowMcKesson

Chris Patterson

• Principal Architect, FellowRelayHealth Intelligence, a part of McKesson• Microsoft MVP (C#, .NET)• Open Source Enthusiast

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• Deconstructing transactions into activities• Orchestrating activities into a distributed transaction• Tracking distributed transactions

Using Transactions For Good

• Atomic completion of operations• Consistency maintained when systems fail• Isolation from concurrent operations• Durability when crashes occur

Taking Transactions Too Far

• Combining two separate transactions using a distributed transaction coordinator• Calling high latency services during a transaction• Using triggers inside a transaction

Creating Inconsistency

Reserve Seat

Process Payment

Reservation Web Site

Deconstructing a Transaction

• A transaction is a sequence of activities that complete entirely, or not at all

Defining an Activity

• An activity should have a single responsibility• An activity may have explicit input arguments• An activity may produce output variables• An activity may update an activity log

Creating an Activity

• An activity should be an autonomous service

Topshelfis an open source framework for creating and deploying .NET services.

Creating an Activity

• An activity should be an autonomous service• An activity should use asynchronous endpoints for availability• An activity should use durable messaging for reliability• An activity should be load balanced for scalability

MassTransitis a free, open-source distributed application framework for .NET. MassTransit makes it easy to create applications and services which leverage message-based, loosely-coupled asynchronous communication for higher availability, reliability, and scalability.

Creating an Itinerary

• An itinerary is a list of activities to be executed

Executing an Itinerary

• An itinerary is executed using a routing slip• A routing slip is a workspace for a distributed transaction

The analogy to a paper routing slipis both obvious and intentional

Creating a Routing Slip

• Activities can be added to the itinerary• Variables may be added to the routing slip

Executing a Routing Slip

• A routing slip is sent to the execute address of the first activity• A routing slip with an empty itinerary completes immediately

Executing an Activity

• An activity is executed using the arguments from the itinerary• An activity’s arguments may be read from the routing slip variables

Completing an Activity

• A completed activity sends the routing slip to the next activity in the itinerary• A completed activity may add or update variables in the routing slip• A completed activity may add an activity log to the routing slip

Completing a Routing Slip

• The routing slip completes when every activity has completed

Publishing Events

Faulting an Activity

• A faulted activity sends the routing slip to the compensate address of the last activity log• A routing slip with no activity log entries faults immediately

Compensating an Activity

• A previously completed activity is compensated using the activity log from the routing slip• A previously completed activity that faults during compensation fails the routing slip

Revising an Itinerary

• A completed activity may revise the itinerary• A completed activity may terminate the routing slip

Tracking a Routing Slip• A routing slip has a unique identifier• An event is published when a routing slip is completed, faulted, or when a routing slip compensation fails• An event is published when a routing slip itinerary is revised• An event is published when a routing slip is terminated

Tracking an Activity

• An activity execution has a unique identifier• An event is published when an activity is completed, faulted, compensated, or when an activity compensation fails

Monitoring a Routing Slip

• A state machine observes routing slip events to track the status of a routing slip

Monitoring a Distributed Transaction

• A state machine maintains separate instances for each transaction• A state machine monitors transaction creation events• A state machine monitors routing slip events to determine when a transaction is completed or faulted

Identifying a Distributed Transaction

• A transaction has a unique identifier• A routing slip event includes the transaction identifier• A transaction event includes the transaction identifier

Retrying Faulted Transactions

• A retry state machine observes transaction fault events• A retry state machine can coordinate additional transaction attempts• A retry state machine may use a retry policy to determine a retry schedule for any additional transaction attempts

Learning Resources

MassTransit• Main Project Site

http://masstransit-project.com

• Documentation Site http://docs.masstransit-project.com

• Source Browser http://source.masstransit-project.com

• GitHub Repository https://github.com/MassTransit

• Build Server https://ci.appveyor.com/project/phatboyg/masstransit