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Overriding Hostnames

When testing services on private or temporary servers, there may not be public DNS pointing to the server IPs. You can override hostnames on macOS using the /etc/hosts file or temporarily with curl --resolve.

macOS Hosts File

The hosts file is located at:

/etc/hosts

You can edit it with sudo privileges:

sudo nano /etc/hosts # use nano

sudo subl /etc/hosts # or use your preferred text editor

Example Entries

Add your custom overrides (IP -> HOST pairs) inside /etc/hosts file:

##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1   localhost
255.255.255.255 broadcasthost
::1             localhost
# Added by Docker Desktop
# To allow the same kube context to work on the host and the container:
127.0.0.1 kubernetes.docker.internal
# End of section

# Custom overrides
192.168.1.100 app.example.com
192.168.1.100 api.example.com
192.168.1.100 dashboard.example.com

Note: Multiple hostnames can point to the same IP. This is useful when a server hosts multiple services.

When you ping or accessing app.example.com, it will resolve to 192.168.1.100:

$ ping app.example.com
PING app.example.com (192.168.1.100): 56 data bytes
Request timeout for icmp_seq 0
...

Testing with curl

Instead of editing the hosts file, you can temporarily map a hostname to an IP using the --resolve option in curl:

curl --resolve app.example.com:443:192.168.1.100 -o /dev/null -v https://app.example.com

Replace the hostname and IP for the service you want to test.

Purpose

  • Resolve hostnames locally without relying on public DNS.
  • Useful for testing, certificate checks, or interacting with services in private or local clusters.
  • Can be done permanently via /etc/hosts or temporarily with curl --resolve.

Flushing DNS Cache

After editing /etc/hosts, flush the DNS cache to apply changes:

sudo dscacheutil -flushcache  
sudo killall -HUP mDNSResponder