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Fluentd plugin to upload logs to Azure Storage append blobs.
 Project Readme


This project is no longer maintained by Microsoft.

Github Repo is still available, so you can fork & develop this project moving forward.


Fluentd out plugin to do something.

Azure Storage Append Blob output plugin buffers logs in local file and uploads them to Azure Storage Append Blob periodically.



gem install fluent-plugin-azure-storage-append-blob


Add following line to your Gemfile:

gem "fluent-plugin-azure-storage-append-blob"

And then execute:



<match pattern>
  type azure-storage-append-blob

  azure_storage_account             <your azure storage account>
  azure_storage_access_key          <your azure storage access key> # leave empty to use MSI
  azure_storage_sas_token           <your azure storage sas token> # leave empty to use MSI
  azure_imds_api_version            <Azure Instance Metadata Service API Version> # only used for MSI
  azure_token_refresh_interval      <refresh interval in min> # only used for MSI
  azure_container                   <your azure storage container>
  auto_create_container             true
  path                              logs/
  azure_object_key_format           %{path}%{time_slice}_%{index}.log
  time_slice_format                 %Y%m%d-%H
  # if you want to use %{tag} or %Y/%m/%d/ like syntax in path / azure_blob_name_format,
  # need to specify tag for %{tag} and time for %Y/%m/%d in <buffer> argument.
  <buffer tag,time>
    @type file
    path /var/log/fluent/azurestorageappendblob
    timekey 120 # 2 minutes
    timekey_wait 60
    timekey_use_utc true # use utc

azure_storage_account (Required)

Your Azure Storage Account Name. This can be retrieved from Azure Management portal.

azure_storage_access_key or azure_storage_sas_token (Either required or both empty to use MSI)

Your Azure Storage Access Key (Primary or Secondary) or shared access signature (SAS) token. This also can be retrieved from Azure Management portal.

If both are empty, the plugin will use the local Managed Identity endpoint to obtain a token for the target storage account.

azure_imds_api_version (Optional, only for MSI)

Default: 2019-08-15

The Instance Metadata Service is used during the OAuth flow to obtain an access token. This API is versioned and specifying the version is mandatory.

See here for more details.

azure_token_refresh_interval (Optional, only for MSI)

Default: 60 (1 hour)

When using MSI, the initial access token needs to be refreshed periodically.

azure_container (Required)

Azure Storage Container name


This plugin creates the Azure container if it does not already exist exist when you set 'auto_create_container' to true. The default value is true


The format of Azure Storage object keys. You can use several built-in variables:

  • %{path}
  • %{time_slice}
  • %{index}

to decide keys dynamically.

%{path} is exactly the value of path configured in the configuration file. E.g., "logs/" in the example configuration above. %{time_slice} is the time-slice in text that are formatted with time_slice_format. %{index} is used only if your blob exceed Azure 50000 blocks limit per blob to prevent data loss. Its not required to use this parameter.

The default format is "%{path}%{time_slice}-%{index}.log".

For instance, using the example configuration above, actual object keys on Azure Storage will be something like:


With the configuration:

azure_object_key_format %{path}/events/ts=%{time_slice}/events.log
path log
time_slice_format %Y%m%d-%H

You get:


The fluent-mixin-config-placeholders mixin is also incorporated, so additional variables such as %{hostname}, etc. can be used in the azure_object_key_format. This is useful in preventing filename conflicts when writing from multiple servers.

azure_object_key_format %{path}/events/ts=%{time_slice}/events-%{hostname}.log


Format of the time used in the file name. Default is '%Y%m%d'. Use '%Y%m%d%H' to split files hourly.

Run tests

gem install bundler
bundle install
bundle exec rake test

Test Fluentd

  1. Create Storage Account and VM with enabled MSI

  2. Setup Docker ang Git

  3. SSH into VM

  4. Download this repo

    git clone
    cd fluent-plugin-azure-storage-append-blob
  5. Build Docker image docker build -t fluent .

  6. Run Docker image with different set of parameters:

    1. STORAGE_ACCOUNT: required, name of your storage account
    2. STORAGE_ACCESS_KEY: storage account access key
    3. STORAGE_SAS_TOKEN: storage sas token with enough permissions for the plugin

    You need to specify STORAGE_ACCOUNT and one of auth ways. If you run it from VM with MSI, just STORAGE_ACCOUNT is required. Keep in mind, there is no way to refresh MSI Token, so ensure you setup proper permissions first.

    docker run -it -e STORAGE_ACCOUNT=<storage> -e STORAGE_ACCESS_KEY=<key> fluent


This project welcomes contributions and suggestions. Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit

When you submit a pull request, a CLA-bot will automatically determine whether you need to provide a CLA and decorate the PR appropriately (e.g., label, comment). Simply follow the instructions provided by the bot. You will only need to do this once across all repos using our CLA.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact with any additional questions or comments.