GCP documentation is not the best one, in my opinion. There are various features that are buried deep inside plethora of api documentations. Stackdriver’s Logging is one of them. Google provides their own altered version of Fluentd in order to send log to Stackdriver. They also require us to run this agent on a GCP or AWS’s services. No other cloud provider is supported. So, in this post I will try to config my fluentd to send log from my own on-prem server to Stackdriver.

The setup

Our Gemfile looks like this

gem "fluentd", '1.6.3'
gem 'fluent-plugin-google-cloud', '0.7.22'

We need to pay attention to the version because fluent-plugin-google-cloud usually requires an older version fluentd.

After that, we bundle install

bundle install --path bundle/vendor

The fluentd config

Basic setup to test our fluentd(send debug tagged event to stdout)

# fluentd.conf
  @type forward
  @id forward_input

<match debug.**>
  @type stdout
  @id stdout_output

Run and test:

bundle exec fluentd -c ./fluentd.conf

# let's send a sample log event using fluent-cat
echo '{"message": "test"}' | be fluent-cat -t debug

Send log to Stackdriver

Official config

The documentation of fluent-plugin-google-cloud instructs us to add a add_insert_ids filter, so we will update our fluentd.conf such as

<filter stackdriver.**>
  @type add_insert_ids

# send all stackdriver.* tagged event to Stackdriver
<match stackdriver.**>
  @type google_cloud

With this config we are good to go if our fluentd runs on an GCP or AWS’s services. If it doesn’t, exception will be raised and we will need ajust fluentd.conf a little bit more.

Send log from any cloud provider services

The reason that the official config doesn’t work on other cloud provider is that fluent-plugin-google-cloud need to pull some meta-data from meta-server. This server is defined as a constant METADATA_SERVICE_ADDR = ''.freeze ref

On our own server, without this meta-service, we will need to provide neccessary meta data. The requires parameters are defined as:


def set_required_metadata_variables

So, out fluentd.conf will become:

<match stackdriver.**>
  @type google_cloud
  use_metadata_service false # this will disable requesting to meta-server
  project_id our-project-id
  zone our-az
  vm_id our-vm-id
  vm_name our-server-hostname

Restart fluentd and send a sample event

echo '{"message": "test"}' | bundle exec fluent-cat -t stackdriver.test

On Stackdriver’s Logs Viewer, the event will be listed inside GCE VM Instance category with instance_id is vm_id that we configured.

The above setting is just minimum required parameters, there are lots more useful one that we can find in fluent-plugin-google-cloud’s source or from Google’s official documentation(though not all of available parameters so we will need to consult source code anyway)