This repository is sample of the exactly-once processing in AzureFunctions environment.
The sample shows how to leverage exactly-once with using CosmosDB as a storage system with communication over HTTP and Azure Storage Queues.
At the code level processing logic gets wrapped into lambda passed to IOnceExecutor<TState>. The executor ensures consistent output - for a given combination of requestId, stateId and TState values the Once method will return exaclty same output. In the sample below for each attemptId and gameId the Once method will always return identical output.
[FunctionName(nameof(ProcessFireAt))]
[return: Queue("attempt-updates")]
public async Task<AttemptMade> ProcessFireAt(
[QueueTrigger("fire-attempt")] FireAt fireAt,
[ExactlyOnce(requestId: "{attemptId}", stateId: "{gameId}")] IOnceExecutor<ShootingRangeState> execute,
ILogger log)
{
log.LogInformation($"Processed startRound: gameId={fireAt.GameId}, position={fireAt.Position}");
var (message, blob) = await execute.Once(sr =>
{
var attemptMade = new AttemptMade
{
AttemptId = fireAt.AttemptId,
GameId = fireAt.GameId
};
if (sr.TargetPosition == fireAt.Position)
{
attemptMade.IsHit = true;
}
else
{
attemptMade.IsHit = false;
}
return (attemptMade, new BlobInfo {BlobName = "This also a side effect"});
});
return message;
}State that is changed inside the function gets stored in CosmosDB. It has to inherit from State object that defines obligatory id and _transactionId fields.
public abstract class State
{
[JsonProperty("id")] public string Id { get; set; }
[JsonProperty("_transactionId")] public Guid? TxId { get; set; }
}
public class ShootingRangeState : State
{
public int TargetPosition { get; set; }
public int NumberOfAttempts { get; set; }
}All intrastructural data used for ensuring the once behavior are stored in a separte collection.
Library requires CosmosClient and IStateStore implementation to be registerd the DI container. In addition, it requires outbox configuration.
var client = new CosmosClient(endpointUri, primaryKey);
builder.Services.AddSingleton(sp => client);
builder.Services.AddSingleton(sp => new CosmosDbStateStore(client, databaseId));
builder.AddExactlyOnce(c =>
{
c.ConfigureOutbox(o =>
{
o.DatabaseId = databaseId;
o.ContainerId = "Outbox";
o.RetentionPeriod = TimeSpan.FromSeconds(30);
});
c.StateStoreIs<CosmosDbStateStore>();
});