Demo Using Consul Template to monitor Changes to Consul KV

title: "Using Consul Template to Monitor Changes in Consul K/V" description: "Step-by-step guide to pull dynamic configuration from Consul K/V store using Consul Template."

In this tutorial, you'll learn how to leverage Consul Template to dynamically fetch configuration values from a Consul K/V store and generate application configuration files automatically. This approach ensures your application configs stay in sync with the latest Consul K/V entries.

1. Populate Consul K/V Store

First, add the required key-value pairs for our eCommerce application. You can verify these entries in Consul UI or via CLI.

Run the following commands:

consul kv put apps/eCommerce/version 4.5
consul kv put apps/eCommerce/environment production
consul kv put apps/eCommerce/database_host customer_db
consul kv put apps/eCommerce/database billing

2. Download and Install Consul Template

Head over to the Consul Template releases page and copy the link for your platform.

Install and verify:

curl -sLo /tmp/consul-template.zip \
  https://releases.hashicorp.com/consul-template/0.25.1/consul-template_0.25.1_linux_amd64.zip

unzip /tmp/consul-template.zip -d /tmp
sudo mv /tmp/consul-template /usr/local/bin/

consul-template -v
# Expected output: consul-template v0.25.1

3. Create a Template File

Define your template with placeholders that map to the Consul K/V keys:

cat << 'EOF' > config.json.tmpl
{
  "environment":   "{{ key "apps/eCommerce/environment" }}",
  "version":       "{{ key "apps/eCommerce/version" }}",
  "database_host": "{{ key "apps/eCommerce/database_host" }}",
  "database_name": "{{ key "apps/eCommerce/database" }}"
}
EOF

Each {{ key "..." }} snippet instructs Consul Template to fetch the corresponding value at render time.

4. Render the Template

Use the -once flag for a single render, or run without it to watch for changes:

consul-template -template "config.json.tmpl:config.json" -once

Verify the output:

ls
cat config.json

{
  "environment": "production",
  "version":     "4.5",
  "database_host": "customer_db",
  "database_name": "billing"
}

5. Next Steps

In production, run Consul Template as a service or sidecar to continuously monitor your K/V store. This ensures that any update in Consul is immediately reflected in your application’s configuration.

Links and References

• Consul Template Documentation
• Consul K/V Store Overview
• HashiCorp Consul Template Releases