Get data with Fluent Bit

Fluent Bit is an open-source agent that collects logs, metrics, and traces from various sources. It allows you to filter, modify, and aggregate event data before sending it to storage. Azure Data Explorer is a fast and highly scalable data exploration service for log and telemetry data. This article guides you through the process of using Fluent Bit to send data to your KQL database.

In this article, you'll learn how to:

• Create a table to store your logs
• Register a Microsoft Entra app with permissions to ingest data
• Configure Fluent Bit to send logs to your table
• Verify that data has landed in your table

Prerequisites

• Fluent Bit.
• A workspace with a Microsoft Fabric-enabled capacity
• A KQL database with ingestion permissions
• A KQL queryset, which will be referred to later as your query environment

Create a table to store your logs

Fluent Bit forwards logs in JSON format with three properties: log (dynamic), tag (string), and timestamp (datetime).

You can create a table with columns for each of these properties. Alternatively, if you have structured logs, you can create a table with log properties mapped to custom columns. To learn more, select the relevant tab.

Default schema

To create a table for incoming logs from Fluent Bit:

1. Browse to your query environment.

2. Select the database where you'd like to create the table.

3. Run the following .create table command:

   .create table FluentBitLogs (log:dynamic, tag:string, timestamp:datetime)
   

   The incoming JSON properties are automatically mapped into the correct column.

Custom schema

To create a table for incoming structured logs from Fluent Bit:

1. Browse to your query environment.

2. Select the database where you'd like to create the table.

3. Run the .create table command. For example, if your logs contain three fields named myString, myInteger, and myDynamic, you can create a table with the following schema:

   .create table FluentBitLogs (myString:string, myInteger:int, myDynamic: dynamic, timestamp:datetime)
   

4. Create a JSON mapping to map log properties to the appropriate columns. The following command creates a mapping based on the example in the previous step:

   .create-or-alter table FluentBitLogs ingestion json mapping "LogMapping" 
       ```[
       {"column" : "myString", "datatype" : "string", "Properties":{"Path":"$.log.myString"}},
       {"column" : "myInteger", "datatype" : "int", "Properties":{"Path":"$.log.myInteger"}}, 
       {"column" : "myDynamic", "datatype" : "dynamic", "Properties":{"Path":"$.log.myInteger"}}, 
       {"column" : "timestamp", "datatype" : "datetime", "Properties":{"Path":"$.timestamp"}} 
       ]```
   

Register a Microsoft Entra app with permissions to ingest data

The Microsoft Entra service principal can be created through the Azure portal or programatically, as in the following example.

This service principal is the identity used by the connector to write data your table in Kusto. You'll later grant permissions for this service principal to access Kusto resources.

1. Sign in to your Azure subscription via Azure CLI. Then authenticate in the browser.

   az login
   

2. Choose the subscription to host the principal. This step is needed when you have multiple subscriptions.

   az account set --subscription YOUR_SUBSCRIPTION_GUID
   

3. Create the service principal. In this example, the service principal is called my-service-principal.

   az ad sp create-for-rbac -n "my-service-principal" --role Contributor --scopes /subscriptions/{SubID}
   

4. From the returned JSON data, copy the appId, password, and tenant for future use.

   {
     "appId": "00001111-aaaa-2222-bbbb-3333cccc4444",
     "displayName": "my-service-principal",
     "name": "my-service-principal",
     "password": "00001111-aaaa-2222-bbbb-3333cccc4444",
     "tenant": "00001111-aaaa-2222-bbbb-3333cccc4444"
   }
   

You've created your Microsoft Entra application and service principal.

Grant permissions to the service principal

Run the following command, replacing <MyDatabase> with the name of the database:

.add database MyDatabase ingestors ('aadapp=<Application (client) ID>;<Directory (tenant) ID>')

This command grants the application permissions to ingest data into your table. For more information, see role-based access control.

Configure Fluent Bit to send logs to your table

To configure Fluent Bit to send logs to your Azure Data Explorer table, create a classic mode or YAML mode configuration file with the following output properties:

Field	Description
Name	azure_kusto
Match	A pattern to match against the tags of incoming records. It's case-sensitive and supports the star (*) character as a wildcard.
Tenant_Id	Directory (tenant) ID from Register a Microsoft Entra app with permissions to ingest data.
Client_Id	Application (client) ID from Register a Microsoft Entra app with permissions to ingest data.
Client_Secret	The client secret key value Register a Microsoft Entra app with permissions to ingest data.
Ingestion_Endpoint	Use the Ingestion URI found in the the KQL database details page. For more information, see Copy URI.
Database_Name	The name of the database that contains your logs table.
Table_Name	The name of the table from Create a table to store your logs.
Ingestion_Mapping_Reference	The name of the ingestion mapping from Create a table. If you didn't create an ingestion mapping, remove the property from the configuration file.

To see an example configuration file, select the relevant tab:

Classic mode

[SERVICE]
    Daemon Off
    Flush 1
    Log_Level trace
    HTTP_Server On
    HTTP_Listen 0.0.0.0
    HTTP_Port 2020
    Health_Check On

[INPUT]
    Name tail
    Path /var/log/containers/*.log
    Tag kube.*
    Mem_Buf_Limit 1MB
    Skip_Long_Lines On
    Refresh_Interval 10

[OUTPUT]
    Name azure_kusto
    Match *
    Tenant_Id azure-tenant-id
    Client_Id azure-client-id
    Client_Secret azure-client-secret
    Ingestion_Endpoint azure-data-explorer-ingestion-endpoint
    Database_Name azure-data-explorer-database-name
    Table_Name azure-data-explorer-table-name

YAML mode

config:
  service: |
    [SERVICE]
        Daemon Off
        Flush 1
        Log_Level trace
        HTTP_Server On
        HTTP_Listen 0.0.0.0
        HTTP_Port 2020
        Health_Check On
        
  inputs: |
    [INPUT]
        Name tail
        Path /var/log/containers/*.log
        multiline.parser docker, cri
        Tag kube.*
        Mem_Buf_Limit 1MB
        Skip_Long_Lines On
        Refresh_Interval 10

  filters: |
    [FILTER]
        Name kubernetes
        Match kube.*
        Merge_Log On
        Merge_Log_key log_processed
        K8S-Logging.Parser On
        K8S-Logging.Exclude Off


  outputs: |
    [OUTPUT]
        Name azure_kusto
    	Match *
    	Tenant_Id azure-tenant-id
    	Client_Id azure-client-id
    	Client_Secret azure-client-secret
    	Ingestion_Endpoint azure-data-explorer-ingestion-endpoint
    	Database_Name azure-data-explorer-database-name
    	Table_Name azure-data-explorer-table-name

Verify that data has landed in your table

Once the configuration is complete, logs should arrive in your table.

1. To verify that logs are ingested, run the following query:

   FluentBitLogs
   | count
   

2. To view a sample of log data, run the following query:

   FluentBitLogs
   | take 100
   

Related content

• Query data in a KQL queryset