Elastic Load Balancing v2: Describe listeners from the CLI

Part 230 of AWS from Zero. This is lesson 5 in the Elastic Load Balancing v2 track.

What we are learning

Use describe-listeners to read or inventory listeners in Elastic Load Balancing v2. This lesson identifies the required input shape, saves the raw response, and keeps inspection separate from execution.

The AWS CLI operation is aws elbv2 describe-listeners. Required operation inputs: none. The modeled top-level response contains Listeners, NextMarker.

Before you run it

aws sts get-caller-identity
REGION="${AWS_REGION:-ap-south-1}"
aws elbv2 describe-listeners help

Use a sandbox account or an approved learning environment. Read the operation help before supplying identifiers, ARNs, network ranges, policy documents, or customer data.

Cost note: Load balancers, LCUs, capacity units, and processed data can incur charges.

The command

aws elbv2 describe-listeners \
  --region "$REGION" \
  --output json > part-230-response.json

The response is saved to part-230-response.json so inspection is separate from execution. The explicit variables above keep required identifiers visible before the API call.

Inspect the result

node -e "const r=require('./part-230-response.json'); console.log(Object.keys(r))"
node -e "const r=require('./part-230-response.json'); console.log(JSON.stringify(r, null, 2))"

Compare the returned identifiers and status fields with the account, Region, and resource you intended to target. For asynchronous operations, continue with the service's matching get, list, or describe command until it reaches a terminal state.

One tiny variation

node -e "const r=require('./part-230-response.json'); console.log(JSON.stringify(r["Listeners"], null, 2))"

This variation changes output inspection rather than adding another infrastructure concept. Keep the raw JSON while developing a query so a narrow projection does not hide an error or unexpected field.

Common mistake

An empty response does not always mean the resource is absent. Confirm the account, Region, pagination behavior, filters, and caller permissions before concluding that nothing exists.

Cleanup

# This operation is read-only, operational, or needs resource-specific rollback.
# Re-read the command output before changing shared infrastructure.
rm -f part-230-request.json part-230-response.json part-230-payload.bin part-230-debug.log

Local request and response files may contain account IDs, ARNs, names, or service configuration. Remove them when the lab is complete and follow dependency-aware cleanup for any AWS resource you created.

Next, we will learn Elastic Load Balancing v2: Describe load balancer attributes from the CLI.

Official AWS CLI reference