Monitoring and understanding the behavior of your applications are essential for performance optimization, which involves aspects like diagnosing issues, debugging, and improving performance. One of the tools for doing this in Azure Cosmos DB is the Response Status Code and the various Failure Metrics.
Response Status Code
Firstly, let’s touch on the response status code. Cosmos DB uses standard HTTP response codes to indicate the status of an API request. Following are some of the commonly seen:
- 200 OK: The request is successful.
- 201 Created: The request has been fulfilled and a new resource has been created as a result.
- 204 No Content: The request has been successful but there’s no representation to return (i.e. the response is empty).
- 409 Conflict: The request could not be completed due to a conflict with the current state of the target resource.
- 429 Too Many Requests: The client has sent too many requests in a given amount of time.
It’s recommended to use retries with exponential backoff for handling transient faults including rate limiting related ones (429). Here’s an example on how to do that (in .NET C#):
private static async Task
{
var backoffPeriod = TimeSpan.FromMilliseconds(100);
const int maxRetries = 6;
HttpResponseMessage response = null;
for (int i = 0; i < maxRetries; i++) { response = await httpClient.SendAsync(httpRequest); if (response.StatusCode == (System.Net.HttpStatusCode)429 && i < maxRetries) { await Task.Delay(backoffPeriod); backoffPeriod *= 2; } else { break; } } return response; }
Failure Metrics
Next, Cosmos DB provides several failure metrics that can be monitored:
- Http 4xx: The count of failed requests due to client-side issues. Review the diagnostics to understand the cause of these failures.
- Http 5xx: The count of failed requests due to server-side issues. Contact Azure support if you experience a high count of 5xx exceptions.
- Rate limit errors: The count of requests that got rate-limited. Review your provisioned throughput and your workload if you experience high rate limit errors.
Analyzing your application’s metrics, understanding the response codes and taking immediate action based on these is a crucial part of application health monitoring using Azure Cosmos DB. A careful study of these response status codes and failure metrics will ensure that you build highly performant and robust applications with Azure Cosmos DB.
Remember, following best practices, using retry policies and appropriately using and understanding response status codes and failure metrics can significantly improve your application’s performance and error handling capabilities while using Azure Cosmos DB. Always refer to the official Microsoft documentation to base your understanding of any new response codes or failure metrics.
Practice Test
The HTTP status code for a successful Cosmos DB operation is always
- True
- False
Answer: False.
Explanation: HTTP status codes for Cosmos DB operations can vary, such as 404 for not found, 429 for too many requests, etc.
If a request fails due to rate limiting in Cosmos DB, the response status code will be
- True
- False
Answer: True.
Explanation: Status code 429 implies that the request rate is large than the provisioned throughput, also known as ‘Too Many Requests’.
The X-ms-status-code header preceded by a minus sign (-) provides the reason for a client-side error in Cosmos DB.
- True
- False
Answer: False.
Explanation: The X-ms-status-code provides details regarding successful operations with Cosmos DB.
Status codes in the 5xx range signify server-side issues in Cosmos DB.
- a) True
- b) False
Answer: a) True
Explanation: HTTP status codes in the 5xx range indicate server-side issues.
The ‘x-ms-retry-after-ms’ header provides information about how long to wait before sending another request.
- True
- False
Answer: True
Explanation: The ‘x-ms-retry-after-ms’ response header indicates the number of milliseconds the client should wait before sending another request.
Request charge in Cosmos DB is measured in Request Units (RUs).
- True
- False
Answer: True
Explanation: Request charge for any operation in Azure Cosmos DB is expressed in Request Units (RUs).
Which of these are valuable for measuring failure metrics in Cosmos DB? [Multiple select]
- a) Status codes
- b) The x-ms-activity-id header
- c) Specific error string contents
- d) Number of retries
Answer: a) Status codes, b) The x-ms-activity-id header, c) Specific error string contents, d) Number of retries
Explanation: Status codes, the ‘x-ms-activity-id’ header, specific error strings, and the number of retries all provide useful context when analyzing failures.
If a request to Cosmos DB exceeds the provisioned throughput, the error message details will be given in the x-ms-retry-after-ms header.
- True
- False
Answer: False
Explanation: The x-ms-retry-after-ms header tells the client how long to wait before retrying the request. The error message details for exceeding provisioned throughput will be obtained from the status code and associated error message.
The status code 404 in Cosmos DB corresponds to which error message?
- a) ‘Not Found’
- b) ‘Too Many Requests’
- c) ‘Conflict’
- d) ‘Gone’
Answer: a) ‘Not Found’
Explanation: The status code 404 implies ‘Not Found’, signifying the requested resource doesn’t exist.
The x-ms-request-charge header represents the number of RUs consumed by a particular operation.
- True
- False
Answer: True
Explanation: The x-ms-request-charge response header provides the number of request units (RUs) that were charged for a particular operation.
Is there a specific status code for unit capacity errors in Cosmos DB?
- True
- False
Answer: True
Explanation: The status code 449 implies ‘Retry With’, signaling that the request should be retried after the specified number of seconds.
Which HTTP response headers are useful for tracing a request in Cosmos DB?
- a) x-ms-activity-id
- b) x-ms-request-charge
- c) x-ms-session-token
- d) x-ms-retry-after-ms
Answer: a) x-ms-activity-id, c) x-ms-session-token
Explanation: The ‘x-ms-activity-id’ and ‘x-ms-session-token’ headers can be used to trace a request in Cosmos DB. The ‘x-ms-activity-id’ provides a unique identifier for the request and ‘x-ms-session-token’ manages consistency.
Interview Questions
What is the HTTP response code that signifies the successful completion of a GET request in Microsoft Azure Cosmos DB?
The HTTP status code 200 OK signifies the successful completion of a GET request in Microsoft Azure Cosmos DB.
What will be the response status code if you try to insert a document with a unique ID which already exists in Azure Cosmos DB?
The response status code will be 409 Conflict if you try to insert a document with a unique ID which already exists.
How is the status of operation represented in Azure Cosmos DB?
In Azure Cosmos DB, the status of operation is represented by HTTP response codes. A 2xx HTTP response code indicates a successful operation, a 4xx code indicates a client-side error, and a 5xx code indicates a server-side error.
What does the 429 status code represent in Azure Cosmos DB?
The 429 status code represents ‘Too Many Requests’. It indicates that the client has been throttled due to exceeding the number of allowed requests in a specific time period.
What is the representation of a client-side error in Azure Cosmos DB?
A client-side error in Azure Cosmos DB is represented by a 4xx HTTP response status code.
What is the representation of a server-side error in Azure Cosmos DB?
A server-side error in Azure Cosmos DB is represented by a 5xx HTTP response status code.
What is the role of failure metrics in Azure Cosmos DB?
In Azure Cosmos DB, failure metrics help monitor application performance by providing detailed insight into failed requests and abnormal operation behavior.
What types of HTTP response code signify an error in Microsoft Azure Cosmos DB operations?
HTTP response codes in the 4xx range signify client-side errors, and the 5xx range indicate server-side errors in Microsoft Azure Cosmos DB operations.
What does the 503 status code mean in Azure Cosmos DB?
A 503 status code in Azure Cosmos DB represents ‘Service Unavailable’. It means that the service is currently unavailable, perhaps due to maintenance or overloading.
What does the 404 status code represent in Azure Cosmos DB?
The 404 status code represents ‘Not Found’. It indicates that the requested resource could not be found in the Azure Cosmos DB.
What is the response status code for the successful completion of a DELETE request in Microsoft Azure Cosmos DB?
The HTTP status code 204 No Content signifies the successful completion of a DELETE request in Microsoft Azure Cosmos DB.
How can you monitor failure metrics in Azure Cosmos DB?
Failure metrics in Azure Cosmos DB can be monitored by using built-in Azure tools like Azure Monitor, Azure Log Analytics, and Azure Application Insights.
What is the response status code for the successful creation of a new resource in Azure Cosmos DB?
The HTTP status code 201 Created signifies the successful creation of a new resource in Azure Cosmos DB.
How do you handle error status codes in Azure Cosmos DB?
Error status codes in Azure Cosmos DB can be handled by checking the HTTP response status code from the service and performing the necessary actions based on the code received.
Which status code indicates a user is unauthorized to perform a particular operation in Azure Cosmos DB?
The HTTP status code 401 Unauthorized indicates that the user is unauthorized to perform the requested operation in Azure Cosmos DB.
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