How to identify the Log-Cache node responsible for a specific source_id

Products

• VMware Tanzu Application Service

Issue/Introduction

Customers may need to identify which specific Log-Cache VM or node is responsible for a given source_id in a Tanzu Application Service (TAS) environment. This is often required for troubleshooting high CPU utilization, memory pressure, or investigating log ingestion issues at the node level.

Cause

Log-Cache uses deterministic routing based on a hash of the source_id. While tools like cf log-meta provide cluster-level visibility, they do not natively expose the specific node mapping for an individual source.

Resolution

To identify if a specific source_id resides on a particular Log-Cache node, you can query the local metadata API on each VM.

1. SSH into a Log-Cache VM: Use BOSH to access one of the Log-Cache instances:

   bosh -d <deployment_name> ssh log-cache/<index>

2. Query the Local Metadata API: Run the following command to retrieve only the metadata stored locally on that specific node:

   curl -k https://localhost:8081/api/v1/meta?localOnly=true

3. Verify the Mapping: Review the output for the target source_id. If the ID is present in the results, that specific node is responsible for handling its logs. If not, repeat the process on other Log-Cache nodes in the cluster until the source is located.