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Study/X-Ray/_X-Ray.md

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+# X-Ray
+[[_X-Ray|AWS X-Ray]] is a [[AWS]] Managed service for diagnosing issues (performance and failures) in a microservice architecture. The main idea is that you pass headers in your calls, [[AWS]] picks up on those headers and looks at the propagation of the requests across bits of [[AWS]].
+
+It's a distributed tracing system. 
+
+## Anatomy of X-Ray 
+
+```mermaid
+flowchart LR
+    API["X-Ray API"] --> Console["X-Ray Console"]
+    Daemon["X-Ray Daemon"] --> API
+    SDK["X-Ray SDK"] --> Daemon
+    Other["Other Clients:\nAWS SDK or AWS CLI"] --> API
+    Other --> Daemon
+    API --> Other
+```
+
+## X-Ray SDK
+- The SDK provides **interceptors** to trace [[HTTP]] requests
+- **Client handlers** to **instrument** AWS SDK clients that your application uses to call other [[AWS]] Services
+- A [[HTTP]] Client to use to instrument calls to other internal and external [[HTTP]] web services
+
+## X-Ray Instrumentation
+Measure the level of product's performance to diagnose errors and write trace information.
+
+## X-Ray-Daemon
+It buffers segments into a queue and uploads in batches.
+It's available to be installed on Linux, Windows, Mac
+Comes with [[_Elastic BeanStalk]] and [[_Lambda]] by default.
+
+## X-Ray Concepts
+* **Segments**:
+    * Details about the host (IP address/kind of host).
+    * Request information.
+    * The time/duration.
+    * Errors and Faults.
+    * Response Statuses.
+
+* **Subsegments**:
+    * More granular timing information.
+    * Can contain calls to other [[AWS]] services.
+
+* **Service Graph**:
+    * Just the UI graph in the Console.
+
+* **Traces**:
+    * A Trace ID is the path of a request through your application.
+    * Gets passed along to everything else, so that it can be tracked.
+    * Not every trace gets recorded.
+
+* **Sampling**:
+    * [[_X-Ray|AWS X-Ray]] uses a sampling algorithm to determine which requests get traced.
+    * Default is:
+        * The first request each second...
+        * And 5% of any additional requests.
+    * Idea is to reduce service charges when you are getting started. The default sampling rate is low.
+    * You can create limits for the rates.
+
+* **Tracing Header**:
+    * All requests are traced up to a configurable minimum.
+    * After that minimum, a percentage of requests are traced to avoid unnecessary cost. (See above)
+    * [The sampling decision and the trace ID are added to HTTP requests in tracing headers named `X-Amzn-Trace-Id`.]{.underline}
+    * The Tracing Header determines if the trace shows up in the viewer.
+
+* **Filter Expressions**:
+    * Applications make a lot of data, you can filter it.
+
+* **Groups**:
+    * Named Filter Expressions.
+    * Groups only update after you update them, the data before still remains. (subsequent traces only)
+
+* **Annotations**:
+    * Up to 50 annotations per trace.
+    * Use to record data that you want to group traces in the console, or when calling the `GetTraceSummaries` API.
+ 
+* **Metadata**:
+    * Metadata are not indexed and values can be any type, including lists and objects.
+    * Use Metadata to record data you want to store in the trace but don't need to use for searching traces.
+
+* **Errors, Faults, and Exceptions**:
+    * X-Ray records the Stack Trace and exception details if available.
+
+## X-Ray Service Integration
+- [[_Lambda|Lambda]]
+- [[_API Gateway|API Gateway]]
+- ELB
+- SNS
+- SQS
+- App Mesh
+- CloudTrail
+- CloudWatch
+- AWS Config
+- EB
+- EC2
+- ECS
+- Fargate
+
+
+
+