Using openssl with the --subject argument allows you to generate certificates without being prompted for any input. This non-interactive mode makes server automation that much easier.

openssl req -x509 -nodes -days 365 -newkey rsa:2048 \
-keyout testapp.key -out testapp.crt \
-subj /C=CA/ST=Quebec/L=Montreal/O=Poutine LLC/OU=devops/CN=*

Subject vars

C ISO country code
ST State/Province/Subdivision
L Locality/City/Town
O Organisation/Company
OU Organisational Unit/Department
CN Common name. The most important! Your domain name! Wildcards supported.