cloud engineer
Here’s how to troubleshoot nameservers with dig.
dig hostname dig domain.com |
To test a specific nameserver.
dig @nameserver hostname dig @nameserver ip-address |
Other options.
dig hostname.domain.com +short dig hostname.domain.com +noall +answer dig @nameserver MX domain.com dig @nameserver AAAA domain.com |
You can use the curl command to test if your load balancer is working as expected. The curl command will alternately and randomly access several instances in your load balancer. If you have 3 instances behind your load balancer, it will be cycled across all 3. The -m1 command means max time is set to 1 second.
while true; do curl -m1 [IP_ADDRESS]; done |
You can test a network port connection using the “nc” command on Linux and “telnet” on Windows.
Format:
$ nc -zv domain.com port
C:\> telnet domain.com port
$ nc -zv domain.com 80 Connection to domain.com 80 port [tcp/http] succeeded! |
C:\> telnet -zv domain.com 80 Connecting To domain.com...Could not open connection to the host, on port 80: Connect failed |
For Telnet, if a connection is successful, it returns no message.
When setting up your cloud infrastructure, you can check if your instances have access to the database by performing this command.
$ nc -zv 10.0.0.45 3306 $ nc -zv domain.com 3306 $ nc -zv endpoint.amazonaws.com 3306 |
If connection has succeeded, you’ll get a message like this in Linux and MacOS …
Connection to endpoint.amazonaws.com 3306 port [tcp/mysql] succeeded! |
On Windows, you can use Telnet to test your DB connection.
C:\>telnet endpoint.amazonaws.com 3306 |
If connection has succeeded, the result is “no message.” If there’s a problem, you’ll get this ….
Connecting To endpoint.amazonaws.com...Could not open
connection to the host, on port 3306: Connect failed |