A simple azure function, triggered by cosmos that logs to blob storage

azure-function-cosmos-trigger.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Microsoft.Azure.Documents;
using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;
using Microsoft.WindowsAzure.Storage.Blob;

namespace CosmosDbChangeFeedTrigger
{
    public static class CosmosDbChangeFeedTrigger
    {
        [FunctionName("<put azure function name here")]
        public static void Run([CosmosDBTrigger(
            "<put database name here>",
            "<put collection name here>",
            ConnectionStringSetting = "<put cosmos db connection string name here",
            LeaseCollectionName = "<put leases collection name here>",
            CreateLeaseCollectionIfNotExists = true)]IReadOnlyList<Document> documents,
            [Blob("test-database-container", FileAccess.Write)] CloudBlobContainer container,
            ILogger log)
        {
            log.LogInformation("Starting the function....");
            log.LogInformation("Saving data...");
            documents.ToList().ForEach(d => writeToBlobStorage(container, d));
            log.LogInformation("Data saved, exiting.");
        }

        private static void writeToBlobStorage(CloudBlobContainer container, Document d)
        {
            var fileName = string.Format("log-file-{0}.json",d.Id);
            Console.WriteLine("Uploading to Blob storage as {0}...", fileName);

            CloudBlockBlob cloudBlockBlob = container.GetBlockBlobReference(fileName);
            cloudBlockBlob.UploadTextAsync(d.ToString()).Wait();
        }
    }
}

The "CosmoDbTrigger" attribute means the function gets triggered when there are changes in a collection. The collection is configured just below the attribute, together with the database that holds the collection

The "Blob" attribute is an "out" binding. Together with the FileAccess enum it gives access to a CloudBlobContainer instance. This instance can be used to access blob storage