Documentation Revamp

Co-authored-by: jbdoumenjou <jb.doumenjou@gmail.com>

docs/content/observability/tracing.md

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+# Tracing
+
+Visualize the Requests Flow
+{: .subtitle }
+
+The tracing system allows developers to visualize call flows in their infrastructure.
+
+Traefik uses OpenTracing, an open standard designed for distributed tracing.
+
+Traefik supports three tracing backends: Jaeger, Zipkin, and DataDog.
+
+## Configuration Reference
+
+??? example "With Jaeger" 
+
+    ```toml
+    # Tracing definition
+    [tracing]
+      # Backend name used to send tracing data
+      #
+      # Default: "jaeger"
+      #
+      backend = "jaeger"
+    
+      # Service name used in Jaeger backend
+      #
+      # Default: "traefik"
+      #
+      serviceName = "traefik"
+        
+      # Span name limit allows for name truncation in case of very long Frontend/Backend names
+      # This can prevent certain tracing providers to drop traces that exceed their length limits
+      #
+      # Default: 0 - no truncation will occur
+      # 
+      spanNameLimit = 0
+    
+      [tracing.jaeger]
+        # Sampling Server URL is the address of jaeger-agent's HTTP sampling server
+        #
+        # Default: "http://localhost:5778/sampling"
+        #
+        samplingServerURL = "http://localhost:5778/sampling"
+    
+        # Sampling Type specifies the type of the sampler: const, probabilistic, rateLimiting
+        #
+        # Default: "const"
+        #
+        samplingType = "const"
+    
+        # Sampling Param is a value passed to the sampler.
+        # Valid values for Param field are:
+        #   - for "const" sampler, 0 or 1 for always false/true respectively
+        #   - for "probabilistic" sampler, a probability between 0 and 1
+        #   - for "rateLimiting" sampler, the number of spans per second
+        #
+        # Default: 1.0
+        #
+        samplingParam = 1.0
+    
+        # Local Agent Host Port instructs reporter to send spans to jaeger-agent at this address
+        #
+        # Default: "127.0.0.1:6831"
+        #
+        localAgentHostPort = "127.0.0.1:6831"
+       
+        # Generate 128-bit trace IDs, compatible with OpenCensus
+        #
+        # Default: false
+        gen128Bit = true
+       
+        # Set the propagation header type. This can be either:
+        #   - "jaeger", jaeger's default trace header.
+        #   - "b3", compatible with OpenZipkin
+        #
+        # Default: "jaeger"
+        propagation = "jaeger"
+    ```
+
+    !!! warning
+        Traefik is only able to send data over the compact thrift protocol to the [Jaeger agent](https://www.jaegertracing.io/docs/deployment/#agent).
+
+??? example "With Zipkin"
+
+    ```toml
+    # Tracing definition
+    [tracing]
+      # Backend name used to send tracing data
+      #
+      # Default: "jaeger"
+      #
+      backend = "zipkin"
+    
+      # Service name used in Zipkin backend
+      #
+      # Default: "traefik"
+      #
+      serviceName = "traefik"
+        
+      # Span name limit allows for name truncation in case of very long Frontend/Backend names
+      # This can prevent certain tracing providers to drop traces that exceed their length limits
+      #
+      # Default: 0 - no truncation will occur
+      # 
+      spanNameLimit = 150
+    
+      [tracing.zipkin]
+        # Zipkin HTTP endpoint used to send data
+        #
+        # Default: "http://localhost:9411/api/v1/spans"
+        #
+        httpEndpoint = "http://localhost:9411/api/v1/spans"
+    
+        # Enable Zipkin debug
+        #
+        # Default: false
+        #
+        debug = false
+    
+        # Use Zipkin SameSpan RPC style traces
+        #
+        # Default: false
+        #
+        sameSpan = false
+    
+        # Use Zipkin 128 bit root span IDs
+        #
+        # Default: true
+        #
+        id128Bit = true
+    
+        # The rate between 0.0 and 1.0 of requests to trace.
+        #
+        # Default: 1.0
+        #
+        sampleRate = 0.2
+    ```
+
+??? example "With DataDog"
+
+    ```toml
+    # Tracing definition
+    [tracing]
+      # Backend name used to send tracing data
+      #
+      # Default: "jaeger"
+      #
+      backend = "datadog"
+    
+      # Service name used in DataDog backend
+      #
+      # Default: "traefik"
+      #
+      serviceName = "traefik"
+      
+      # Span name limit allows for name truncation in case of very long Frontend/Backend names
+      # This can prevent certain tracing providers to drop traces that exceed their length limits
+      #
+      # Default: 0 - no truncation will occur
+      # 
+      spanNameLimit = 100
+    
+      [tracing.datadog]
+        # Local Agent Host Port instructs reporter to send spans to datadog-tracing-agent at this address
+        #
+        # Default: "127.0.0.1:8126"
+        #
+        localAgentHostPort = "127.0.0.1:8126"
+    
+        # Enable DataDog debug
+        #
+        # Default: false
+        #
+        debug = false
+    
+        # Apply shared tag in a form of Key:Value to all the traces
+        #
+        # Default: ""
+        #
+        globalTag = ""
+    ```
+    
+??? example "With Instana"
+
+    ```toml
+    # Tracing definition
+    [tracing]
+      # Backend name used to send tracing data
+      #
+      # Default: "jaeger"
+      #
+      backend = "instana"
+      # Service name used in Instana backend
+      #
+      # Default: "traefik"
+      #
+      serviceName = "traefik"
+      [tracing.instana]
+        # Local Agent Host instructs reporter to send spans to instana-agent at this address
+        #
+        # Default: "127.0.0.1"
+        #
+        localAgentHost = "127.0.0.1"
+        # Local Agent port instructs reporter to send spans to the instana-agent at this port
+        # 
+        # Default: 42699
+        #
+        localAgentPort = 42699
+        # Set Instana tracer log level
+        #
+        # Default: info
+        # Valid values for logLevel field are:
+        #   - error
+        #   - warn
+        #   - debug
+        #   - info
+        #
+        logLevel = "info"
+    ```