# 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 he 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
- ELB
- SNS
- SQS
- App Mesh
- CloudTrail
- CloudWatch
- AWS Config
- EB
- EC2
- ECS
- Fargate