This repository shows how to use exactly-once processing in AzureFunctions environment.
The sample shows how to leverage exactly-once with state stored in CosmosDB and communication over HTTP and Azure Storage Queues.
At the code level processing logic gets wrapped into lambda passed to the exaclty-once library. The library makes consistent output ie. exaclty the same for duplicated and out-of-order executions. For example, in the sinppet below (message, blog) tuple will be consistently returned:
var (message, blob) = await execute
.Once<FireAt>(fireAt.AttemptId)
.On<ShootingRangeState>(fireAt.GameId)
.WithOutput(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"});
});State that is change by the functions and stored in CosmosDB is a POCO with obligatory id field _transactionId. All other intrastructural data is stored in a separate collection.
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; }
}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>();
});