in_amqp: Add documentation for in_amqp plugin

Author: matwey

pipeline/inputs/amqp.md

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+# AMQP
+
+The _AMQP_ input plugin allows Fluent Bit to consume messages from an AMQP broker such as RabbitMQ. It connects to the specified broker, consumes messages from a queue, and processes them as log records.
+
+## Configuration parameters
+
+The plugin supports the following configuration parameters:
+
+| Key | Description | Default |
+|:---|:---|:---|
+| `uri` | Specify an AMQP URI to connect to the broker | `amqp://` |
+| `queue` | Specify an AMQP queue name to consume from | _none_ (required) |
+| `parser` | Specify a parser to process the message payload | _none_ |
+| `reconnect.retry_limits` | Maximum number of retries to connect to the broker | `5` |
+| `reconnect.retry_interval` | Retry interval (in seconds) to connect to the broker | `60` |
+
+## How it works
+
+The AMQP input plugin connects to an AMQP broker and consumes messages from a specified queue. Each message is processed and converted into a Fluent Bit log record with the following characteristics:
+
+1. The message body becomes the main content of the record
+2. AMQP message properties (like content type, routing key, etc.) are added as metadata
+3. AMQP message headers are added as a nested metadata field
+4. If a parser is specified, it's applied to the message body
+
+### Message Properties Mapping
+
+The following AMQP message properties are mapped to Fluent Bit record metadata:
+
+- `routing_key` - The routing key used to route the message to the queue
+- `content_type` - The MIME content type of the message
+- `content_encoding` - The content encoding of the message
+- `correlation_id` - Application correlation identifier
+- `reply_to` - Address to reply to
+
+### Message Headers
+
+AMQP message headers are mapped to a `headers` field in the record metadata as a key-value map.
+
+## Get started
+
+To consume messages from an AMQP broker, you can run the plugin from the command line or through the configuration file.
+
+### Command line
+
+The following command will start Fluent Bit with the AMQP input plugin:
+
+```shell
+fluent-bit -i amqp -p queue=my_queue -o stdout
+```
+
+### Configuration file
+
+In your main configuration file, append the following sections:
+
+{% tabs %}
+{% tab title="fluent-bit.yaml" %}
+
+```yaml
+pipeline:
+  inputs:
+    - name: amqp
+      queue: my_queue
+      uri: amqp://guest:guest@localhost:5672/%2F
+
+  outputs:
+    - name: stdout
+      match: '*'
+```
+
+{% endtab %}
+{% tab title="fluent-bit.conf" %}
+
+```text
+[INPUT]
+  Name  amqp
+  Queue my_queue
+  URI   amqp://guest:guest@localhost:5672/%2F
+
+[OUTPUT]
+  Name  stdout
+  Match *
+```
+
+{% endtab %}
+{% endtabs %}
+
+## Example: Consuming JSON messages
+
+If your AMQP messages contain JSON data, you can use a parser to process them:
+
+{% tabs %}
+{% tab title="fluent-bit.yaml" %}
+
+```yaml
+pipeline:
+  inputs:
+    - name: amqp
+      queue: json_messages
+      parser: json
+      uri: amqp://guest:guest@localhost:5672/%2F
+
+  parsers:
+    - name: json
+      format: json
+
+  outputs:
+    - name: stdout
+      match: '*'
+```
+
+{% endtab %}
+{% tab title="fluent-bit.conf" %}
+
+```text
+[INPUT]
+  Name  amqp
+  Queue json_messages
+  Parser json
+  URI   amqp://guest:guest@localhost:5672/%2F
+
+[PARSER]
+  Name   json
+  Format json
+
+[OUTPUT]
+  Name  stdout
+  Match *
+```
+
+{% endtab %}
+{% endtabs %}
+
+## Connection Management
+
+The plugin handles connection failures gracefully:
+
+1. If the initial connection fails, it will retry based on `reconnect.retry_limits` and `reconnect.retry_interval`
+2. If a connection is lost during operation, the plugin will automatically attempt to reconnect
+3. Messages consumed but not yet processed will be requeued by the broker (assuming proper acknowledgment settings)
+
+## Requirements
+
+The AMQP input plugin requires the RabbitMQ C client library (rabbitmq-c) to be installed on the system.