Contents

Overview

Each HTTP connection that your client makes results in a certain amount of overhead. The Autoscaler API supports batching, to allow your client to put several API calls into a single HTTP request.

Examples of situations when you might want to use batching:

• You've just started using the API and you have a lot of data to upload.
• A user made changes to data while your application was offline (disconnected from the Internet), so your application needs to synchronize its local data with the server by sending a lot of updates and deletes.

In each case, instead of sending each call separately, you can group them together into a single HTTP request.

You're limited to 1000 calls in a single batch request. If you need to make more calls than that, use multiple batch requests.

Note : The batch system for the Autoscaler API uses the same syntax as the OData batch processing system, but the semantics differ.

Batch details

A batch request consists of multiple API calls combined into one HTTP request. This section describes the batch syntax in detail; later, there's an example .

Note : A set of n requests batched together counts toward your usage limit as n requests, not as one request. The batch request is taken apart into a set of requests before processing.

Format of a batch request

A batch request is a single standard HTTP request containing multiple Autoscaler API calls, using the multipart/mixed content type. Within that main HTTP request, each of the parts contains a nested HTTP request.

Each part begins with its own Content-Type: application/http HTTP header. It can also have an optional Content-ID header. However, the part headers are just there to mark the beginning of the part; they're separate from the nested request. After the server unwraps the batch request into separate requests, the part headers are ignored.

The body of each part is itself a complete HTTP request, with its own verb, URL, headers, and body.

The HTTP headers for the outer batch request, except for the Content- headers such as Content-Type , apply to every request in the batch. If you specify a given HTTP header in both the outer request and an individual call, then the individual call header's value overrides the outer batch request header's value. The headers for an individual call apply only to that call.

For example, if you provide an Authorization header for a specific call, then that header applies only to that call. If you provide an Authorization header for the outer request, then that header applies to all of the individual calls unless they override it with Authorization headers of their own.

When the server receives the batched request, it applies the outer request's query parameters and headers (as appropriate) to each part, and then treats each part as if it were a separate HTTP request.

Response to a batch request

The server's response is a single standard HTTP response with a multipart/mixed content type; each part is the response to one of the requests in the batched request, in the same order as the requests.

Like the parts in the request, each response part contains a complete HTTP response, including a status code, headers, and body. And like the parts in the request, each response part is preceded by a Content-Type header that marks the beginning of the part.

If a given part of the request had a Content-ID header, then the corresponding part of the response has a matching Content-ID header, with the original value preceded by the string response- , as shown in the following example.

Note : The server may perform your calls in any order. Don't count on their being executed in the order in which you specified them. If you want to ensure that two calls occur in a given order, you can't send them in a single request; instead, send the first one by itself, then wait for the response to the first one before sending the second one.

Example

The following example shows the use of batching with a generic (fictional) demo API called the Farm API. However, the same concepts apply to the Autoscaler API.

Example batch request

POST /batch HTTP/1.1
Authorization: Bearer your_auth_token
Host: host
Content-Type: multipart/mixed; boundary=batch_foobarbaz
Content-Length: total_content_length

--batch_foobarbaz
Content-Type: application/http
Content-ID: <item1:[email protected]>

GET /farm/v1/animals/pony