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Setup Development Environment

CoreDNS-GSLB provides a comprehensive local development environment using Docker Compose. This environment spins up CoreDNS configured with the GSLB plugin along with dummy web applications to simulate routing, health checks, failovers, and GeoIP/ECS features.

Prerequisites

  • Docker and Docker Compose installed.
  • dig command-line tool (usually part of dnsutils or bind-utils) for DNS queries.

Note: TLS certificates are generated on-demand for TLS and mTLS validation. See the cert_gen folder and the webapp init.sh for details.

Starting the Dev Stack

  1. Build CoreDNS containing the GSLB plugin: 

    sudo docker compose -f docker-compose.dev.yml --progress=plain build

  2. Start the stack (CoreDNS + webapp nodes): 

    sudo docker compose -f docker-compose.dev.yml up -d

Verifying and Simulating Workloads

1. Basic DNS Resolution

Verify that CoreDNS is resolving records properly: 

dig -p 8053 @127.0.0.1 webapp.app-x.gslb.example.com +short
Expected output: 172.16.0.10

2. Simulating a Failover

Stop the primary webapp container (webapp10) to trigger an unhealthy backend status: 

sudo docker compose -f docker-compose.dev.yml stop webapp10

Wait for the health check scrape interval (approx. 30 seconds), then query again: 

dig -p 8053 @127.0.0.1 webapp.app-x.gslb.example.com +short
Expected output: 172.16.0.11 (automatically failed over to the secondary backend).

Now start the primary container again: 

sudo docker compose -f docker-compose.dev.yml start webapp10
Wait a few seconds, then resolve again to observe the traffic routing switch back: 
dig -p 8053 @127.0.0.1 webapp.app-x.gslb.example.com +short
Expected output: 172.16.0.10

Testing EDNS Client Subnet (ECS) & GeoIP

You can simulate DNS queries originating from different regions to test the GeoIP routing engine.

1. Subnet Location-based Routing

Simulate a query coming from subnet 10.1.0.0/24: 

dig -p 8053 @127.0.0.1 webapp-geoip-loc.app-y.gslb.example.com +short +subnet=10.1.0.42/24
Expected output: 172.16.0.10

Simulate a query coming from subnet 10.2.0.0/24: 

dig -p 8053 @127.0.0.1 webapp-geoip-loc.app-y.gslb.example.com +short +subnet=10.2.0.7/24
Expected output: 172.16.0.11

2. Country-based Routing

Simulate a query coming from a US IP address (8.8.8.8): 

dig -p 8053 @127.0.0.1 webapp-geoip-country.app-y.gslb.example.com +short +subnet=8.8.8.8/24
Expected output: 172.16.0.11

Simulate a query coming from a French IP address (90.0.0.0): 

dig -p 8053 @127.0.0.1 webapp-geoip-country.app-y.gslb.example.com +short +subnet=90.0.0.0/24
Expected output: 172.16.0.10

Starting the HA Sync (Redis) Dev Stack

If you are developing or testing the high-availability synchronization features (shared health states, locks, pub/sub propagation), you should use the dedicated HA Docker Compose configuration:

  1. Build the HA dev stack: 

    sudo docker compose -f docker-compose.redis.yml build

  2. Start the HA dev stack (Redis + 2 CoreDNS instances + webapps): 

    sudo docker compose -f docker-compose.redis.yml up -d

Stopping the Dev Stack

To stop and remove all container resources (including volume cleanup):

  • For the Basic Dev Stack: 

    sudo docker compose -f docker-compose.dev.yml down -v

  • For the HA Dev Stack: 

    sudo docker compose -f docker-compose.redis.yml down -v