diff --git a/infra/functions.bicep b/infra/functions.bicep
index e86ff08..8b88313 100644
--- a/infra/functions.bicep
+++ b/infra/functions.bicep
@@ -144,12 +144,8 @@ resource functionApp 'Microsoft.Web/sites@2021-02-01' = {
           value: imageStorageSettings.folderPath
         }
         {
-          name: '${imageIndexStorageKey}__ConnectionString'
-          value: imageStorageSettings.connectionString
-        }
-        {
-          name: '${imageIndexStorageKey}__ContainerName'
-          value: 'index'
+          name: '${imageIndexStorageKey}__BlobContainerUri'
+          value: '${functionStorageAccount.properties.primaryEndpoints.blob}index'
         }
       ]
     }
diff --git a/infra/main.bicep b/infra/main.bicep
index fbd1923..e40f61d 100644
--- a/infra/main.bicep
+++ b/infra/main.bicep
@@ -54,8 +54,7 @@ resource container 'Microsoft.Storage/storageAccounts/blobServices/containers@20
 }
 
 var imageSettings = {
-  connectionString: 'DefaultEndpointsProtocol=https;AccountName=${imageStorage.name};EndpointSuffix=${az.environment().suffixes.storage};AccountKey=${imageStorage.listKeys().keys[0].value}'
-  blobContainerUri: '${imageStorage.properties.primaryEndpoints.blob}/${imageContainerName}'
+  blobContainerUri: '${imageStorage.properties.primaryEndpoints.blob}${imageContainerName}'
   folderPath: 'root'
 }
 
@@ -72,18 +71,17 @@ module functions 'functions.bicep' = {
   }
 }
 
-// TODO refactor this. this should only require reading permission. Image INDEX requires more permissions and currently these are in same place
 // TODO Also this assignment could probably be a separate module etc.
-var storageBlobDataOwnerRoleDefinitionId = 'b7e6dc6d-f1e8-4753-8033-0f276bb0955b'
+var storageBlobDataReaderRoleDefinitionId = '2a2b9908-6ea1-4ae2-8e65-a410df84e7d1'
 resource functionAppFunctionBlobStorageAccess 'Microsoft.Authorization/roleAssignments@2022-04-01' = {
-  scope: imageStorage
-  name: guid(functions.name, storageBlobDataOwnerRoleDefinitionId, imageStorage.id)
+  scope: container
+  name: guid(functions.name, storageBlobDataReaderRoleDefinitionId, container.id)
   properties: {
     principalId: functions.outputs.functionAppPrincipalId
     principalType: 'ServicePrincipal'
     roleDefinitionId: subscriptionResourceId(
       'Microsoft.Authorization/roleDefinitions',
-      storageBlobDataOwnerRoleDefinitionId
+      storageBlobDataReaderRoleDefinitionId
     )
   }
 }
diff --git a/infra/types.bicep b/infra/types.bicep
index 3bd40d9..78e415c 100644
--- a/infra/types.bicep
+++ b/infra/types.bicep
@@ -8,6 +8,5 @@ type DiscordSettings = {
 @export()
 type ImageStorageSettings = {
   blobContainerUri: string
-  connectionString: string
   folderPath: string
 }
diff --git a/src/Common/BlobStorageImageService/BlobStorageImageSourceOptions.cs b/src/Common/BlobStorageImageService/BlobStorageImageSourceOptions.cs
index 16a7e32..15047cc 100644
--- a/src/Common/BlobStorageImageService/BlobStorageImageSourceOptions.cs
+++ b/src/Common/BlobStorageImageService/BlobStorageImageSourceOptions.cs
@@ -17,6 +17,7 @@ public class BlobStorageImageSourceOptions
 
     /// <summary>
     /// The name of the container where the images are stored.
+    /// This is not needed (nor used) if BlobContainerUri is used.
     /// </summary>
     public required string? ContainerName { get; set; }
 
diff --git a/src/Common/IndexService/BlobStorageIndexStorageService.cs b/src/Common/IndexService/BlobStorageIndexStorageService.cs
index e063027..c263bd7 100644
--- a/src/Common/IndexService/BlobStorageIndexStorageService.cs
+++ b/src/Common/IndexService/BlobStorageIndexStorageService.cs
@@ -2,29 +2,32 @@
 using Azure.Storage.Blobs;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
 
 namespace DiscordImagePoster.Common.IndexService;
 
 public class BlobStorageIndexStorageService : IIndexStorageService
 {
-    private ILogger<BlobStorageIndexStorageService> _logger;
+    private readonly ILogger<BlobStorageIndexStorageService> _logger;
+    private readonly ImageIndexOptions _options;
     private readonly BlobContainerClient _blobContainerClient;
 
-    private const string IndexBlobName = "index.json";
-
     public BlobStorageIndexStorageService
     (
         ILogger<BlobStorageIndexStorageService> logger,
+        IOptions<ImageIndexOptions> options,
         [FromKeyedServices(KeyedServiceConstants.ImageIndexBlobContainerClient)] BlobContainerClient blobContainerClient
     )
     {
         _logger = logger;
+        _options = options.Value;
         _blobContainerClient = blobContainerClient;
     }
 
     public async Task<ImageIndex?> GetImageIndexAsync()
     {
-        var blobClient = _blobContainerClient.GetBlobClient(IndexBlobName);
+        _logger.LogTrace("Getting image index from {IndexFileName}", _options.IndexFileName);
+        var blobClient = _blobContainerClient.GetBlobClient(_options.IndexFileName);
         var exists = await blobClient.ExistsAsync();
         if (!exists)
         {
@@ -38,9 +41,10 @@ public BlobStorageIndexStorageService
 
     public async Task UpdateIndexAsync(ImageIndex index)
     {
+        _logger.LogTrace("Updating image index to {IndexFileName}", _options.IndexFileName);
         await _blobContainerClient.CreateIfNotExistsAsync();
         var bytes = JsonSerializer.SerializeToUtf8Bytes(index);
-        var blobClient = _blobContainerClient.GetBlobClient(IndexBlobName);
+        var blobClient = _blobContainerClient.GetBlobClient(_options.IndexFileName);
         await blobClient.UploadAsync(new MemoryStream(bytes), true);
     }
 }
diff --git a/src/Common/IndexService/ImageIndexOptions.cs b/src/Common/IndexService/ImageIndexOptions.cs
index 531dee2..e28ca08 100644
--- a/src/Common/IndexService/ImageIndexOptions.cs
+++ b/src/Common/IndexService/ImageIndexOptions.cs
@@ -11,12 +11,25 @@ public class ImageIndexOptions
 {
     /// <summary>
     /// The connection string to the Azure Storage account.
+    /// Use this only for development. Use managed identity in production.
     /// </summary>
     public required string ConnectionString { get; set; }
 
     /// <summary>
-    /// Container name where the index is stored.
+    /// The name of the container where the images are stored.
+    /// This is not needed (nor used) if BlobContainerUri is used.
     /// </summary>
-    [Required]
-    public required string ContainerName { get; set; }
+    public required string? ContainerName { get; set; }
+
+    /// <summary>
+    /// The URI to the container where the images are stored.
+    /// https://{account_name}.blob.core.windows.net/{container_name}
+    /// 
+    /// If this is used, the ConnectionString is not needed and managed identity is used
+    /// </summary>
+    public required string? BlobContainerUri { get; set; }
+
+    /// <summary>
+    /// The path to the index file. Defaults to index.json in root.
+    public required string IndexFileName { get; set; } = "index.json";
 }
diff --git a/src/FunctionApp.Isolated/Program.cs b/src/FunctionApp.Isolated/Program.cs
index faa4dfc..cc233ff 100644
--- a/src/FunctionApp.Isolated/Program.cs
+++ b/src/FunctionApp.Isolated/Program.cs
@@ -36,7 +36,6 @@
 
         services.AddKeyedTransient(KeyedServiceConstants.ImageBlobContainerClient, (services, _) =>
         {
-            //https://{account_name}.blob.core.windows.net/{container_name}
             var options = services.GetRequiredService<IOptions<BlobStorageImageSourceOptions>>().Value;
             if (!string.IsNullOrWhiteSpace(options.BlobContainerUri))
             {
@@ -48,6 +47,10 @@
         services.AddKeyedTransient(KeyedServiceConstants.ImageIndexBlobContainerClient, (services, _) =>
         {
             var options = services.GetRequiredService<IOptions<ImageIndexOptions>>().Value;
+            if (!string.IsNullOrWhiteSpace(options.BlobContainerUri))
+            {
+                return new BlobContainerClient(new Uri(options.BlobContainerUri), new DefaultAzureCredential());
+            }
             return new BlobContainerClient(options.ConnectionString, options.ContainerName);
         });