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Promtail

Cloud setup GCP Logs

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Cloud setup GCP logs

This document explain how one can setup Google Cloud Platform to forward its cloud resource logs from a particular GCP project into Google Pubsub topic so that is available for Promtail to consume.

This document assumes, that reader have gcloud installed and have required permissions(as mentioned in Roles and Permission section).

There’s two flavours of how to configure this:

Pull-based subscription: Promtail pulls log entries from a GCP PubSub topic
Push-based subscription: GCP sends log entries to a web server that Promtail listens

Overall, the setup between GCP, Promtail and Loki will look like the following:

Roles and Permission

User should have following roles to complete the setup.

“roles/pubsub.editor”
“roles/logging.configWriter”

Setup Pubsub Topic

Google Pubsub Topic will act as the queue to persist log messages which then can be read from Promtail.

$ gcloud pubsub topics create $TOPIC_ID

e.g:

$ gcloud pubsub topics create cloud-logs

Setup Log Router

We create a log sink to forward cloud logs into pubsub topic created before

$ gcloud logging sinks create $SINK_NAME $SINK_LOCATION $OPTIONAL_FLAGS

e.g:

$ gcloud logging sinks create cloud-logs pubsub.googleapis.com/projects/my-project/topics/cloud-logs \
--log-filter='resource.type=("gcs_bucket")' \
--description="Cloud logs"

Above command also adds log-filter option which represents what type of logs should get into the destination pubsub topic. For more information on adding log-filter refer this document

We cover more advanced log-filter below

Grant log sink the pubsub publisher role

Find the writer identity service account of the log sink just created:

gcloud logging sinks describe \
 --format='value(writerIdentity)' $SINK_NAME

For example:

gcloud logging sinks describe \
 --format='value(writerIdentity)' cloud-logs

Create an IAM policy binding to allow log sink to publish messages to the topic:

gcloud pubsub topics add-iam-policy-binding $TOPIC_ID \
--member=$WRITER_IDENTITY --role=roles/pubsub.publisher

For example:

gcloud pubsub topics add-iam-policy-binding cloud-logs \
--member=serviceAccount:pxxxxxxxxx-xxxxxx@gcp-sa-logging.iam.gserviceaccount.com --role=roles/pubsub.publisher

Create Pubsub subscription for Grafana Loki

Pull

We create subscription for the pubsub topic we create above and Promtail uses this subscription to consume log messages.

$ gcloud pubsub subscriptions create cloud-logs --topic=$TOPIC_ID \
--ack-deadline=$ACK_DEADLINE \
--message-retention-duration=$RETENTION_DURATION \

e.g:

$ gcloud pubsub subscriptions create cloud-logs --topic=projects/my-project/topics/cloud-logs \
--ack-deadline=10 \
--message-retention-duration=7d

For more fine grained options, refer to the gcloud pubsub subscriptions --help

Push

Since GCP PubSub push subscriptions is a rather new service, one needs to grant Google a permission in some cases. First, check the date the GCP project was created on:

> gcloud projects describe $GCP_PROJECT_ID

createTime: 'some date'
...
projectId: $GCP_PROJECT_ID
projectNumber: '$GCP_PROJECT_NUMBER'

If the createTime is later than April 8, 2021, skip the following step. Otherwise, you need to grant the iam.serviceAccountTokenCreator role to a Google-managed service account:

PUBSUB_SERVICE_ACCOUNT="service-${GCP_PROJECT_NUMBER}@gcp-sa-pubsub.iam.gserviceaccount.com"
gcloud projects add-iam-policy-binding ${GCP_PROJECT_ID} \
 --member="serviceAccount:${PUBSUB_SERVICE_ACCOUNT}"\
 --role='roles/iam.serviceAccountTokenCreator'

Having configured Promtail with the GCP Logs Push target, hosted in an internet-facing and HTTPS enabled deployment, we can continue with creating the push subscription.

gcloud pubsub subscriptions create cloud-logs \
--topic=$TOPIC_ID \
--push-endpoint=$HTTPS_PUSH_ENDPOINT_URI

ServiceAccount for Promtail

We need a service account with following permissions.

pubsub.subscriber

This enables Promtail to read log entries from the pubsub subscription created before.

you can find example for Promtail scrape config for gcplog here

If you are scraping logs from multiple GCP projects, then this serviceaccount should have above permissions in all the projects you are tyring to scrape.

Operations

Sometimes you may wish to clear the pending pubsub queue containing logs.

These messages stays in Pubsub Subscription until they’re acknowledged. The following command removes log messages without needing to be consumed via Promtail or any other pubsub consumer.

gcloud pubsub subscriptions seek <subscription-path> --time=<yyyy-mm-ddThh:mm:ss>

To delete all the old messages until now, set --time to current time.

gcloud pubsub subscriptions seek projects/my-project/subscriptions/cloud-logs --time=$(date +%Y-%m-%dT%H:%M:%S)

Advanced log filter

So far we’ve covered admitting GCS bucket logs into Grafana Loki, but often one may need to add multiple cloud resource logs and may also need to exclude unnecessary logs. The following is a more complex example.

We use the log-filter option to include logs and the exclusion option to exclude them.

Use Case

Include following cloud resource logs

GCS bucket
Kubernetes
IAM
HTTP Load balancer

And we exclude specific HTTP load balancer logs based on payload and status code.

$ gcloud logging sinks create cloud-logs pubsub.googleapis.com/projects/my-project/topics/cloud-logs \
--log-filter='resource.type=("gcs_bucket OR k8s_cluster OR service_account OR iam_role OR api OR audited_resource OR http_load_balancer")' \
--description="Cloud logs" \
--exclusion='name=http_load_balancer,filter=<<EOF
resource.type="http_load_balancer"
(
	(
		jsonPayload.statusDetails=("byte_range_caching" OR "websocket_closed")
	)
		OR
	(
		http_request.status=(101 OR 206)
	)
)
EOF