When a cache miss occurs, the content must be retrieved from the origin. To the origin, this appears as a web request. The origin may return an HTTP error code (4xx or 5xx status codes). You can monitor, alarm, and receive notifications that include these HTTP response codes. CloudFront publishes six metrics with a one-minute granularity into Amazon CloudWatch:
Requests: Total HTTP and HTTPS requests received.
Bytes Downloaded: Total data downloaded by clients.
Bytes Uploaded: Total data uploaded to your origin.
4xx Error Rate: Percentage of requests that result in a 400-type response.
5xx Error Rate: Percentage of requests that result in a 500-type response.
Total Error Rate: Percentage of requests that result in a 400-type or 500-type response.
You can monitor HTTP response codes that are returned from the origin using the 4xx Error Rate, 5xx Error Rate, and Total Error Rate metrics.
Answer these questions. The answers follow the last question. If you cannot answer these questions correctly, consider reading this section again until you can.
1. You need to monitor the total HTTP response codes from the origin that result in a 4xx or 5xx error. Which metric should you use?
A. Cache hit rate
B. Healthy host count
C. Total error rate
D. HTTP error rate
2. The TTL has expired on an object that is cached by a CloudFront distribution. However, the cached file still matches the most current version in the origin. How will CloudFront handle the next request for this file?
A. CloudFront forwards the request to the origin server, which returns the status code 304 Not Modified.
B. CloudFront forwards the request to the origin server, which returns the status code 200 OK.
C. CloudFront forwards the request to the origin server, which returns the status code 304 Not Modified and sends the latest version of the file to the CloudFront distribution.
D. CloudFront forwards the request to the origin server, which returns the status code 200 OK and sends the latest version of the file to the CloudFront distribution.
1. Answer: C is correct. The percentage of requests to the origin that result in a 4xx or 5xx error is shown in the total error rate.
2. Answer: A is correct. When the TTL on a file expires, CloudFront forwards the next incoming request to the origin server. If CloudFront has the latest version, the origin returns the status code 304 Not Modified.
This section covers the following objective of Domain 5 (Networking and Content Delivery) from the official AWS Certified SysOps Administrator – Associate (SOA-C02) exam guide:
5.3 Troubleshoot network connectivity issues
If you can correctly answer these questions before going through this section, save time by skimming the Exam Alerts in this section and then completing the Cram Quiz at the end of the section.
1. What task must be completed by the colocation provider for Direct Connect physical connectivity to be established?
2. A VPN connection establishment is failing during phase 1. What are some possible causes of this issue?
1. Answer: A cross-connect must be made between your device and the Direct Connect hardware.
2. Answer: IKE negotiation may fail due to a physical customer gateway that does not meet the AWS VPN requirements. Also a misconfigured preshared key prevents phase 1 from completing.
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