Nmap is an all-purpose network and port scanner. It can scan hundreds of hosts and ports quickly, across a variety of protocols and situations. Here are a few basic commands that you can use:
Check that ports 8200 and 8201 are listening on a host. The Pn flag tells nmap to skip the preliminary ping to see if the host is up.
nmap -p 8200,8201 10.0.1.10 -Pn
Tcpdump lets you see raw TCP packets coming across a network interface on the machine. This can be helpful when you need to determine whether traffic is even reaching a host and what it looks like.
Show all traffic on port 8201 except from the load balancer at 10.0.1.117. Do not resolve hostnames and ports into names, leave them as numbers (-nn)
tcpdump -nn port 8201 and not host 10.0.1.117
Capture everything on the eth0 interface
tcpdump -i eth0
The openssl command can be used to inspect an SSL certificate to see if it is valid and check its configuration: https://www.sslshopper.com/article-most-common-openssl-commands.html
Check a certificate
openssl x509 -in certificate.crt -text -noout
Check a private key
openssl rsa -in privateKey.key -check
Create a new SSL certificate for your domain or subdomain. Must be able to create DNS records in your domain to do this:
Wildcard cert for all of hashidemos.io
certbot certonly --server https://acme-v02.api.letsencrypt.org/directory --manual --preferred-challenges dns-01 -d *.hashidemos.io
Cert for foo.hashidemos.io and bar.hashidemos.io
certbot certonly --server https://acme-v02.api.letsencrypt.org/directory --manual --preferred-challenges dns-01 -d foo.hashidemos.io -d bar.hashidemos.io