That is possible. You will need to specify a certain route for each app.
For example,
foo.com/ -> PHP
foo.com/api -> Flask App
A sample apache config would be something like this:
<VirtualHost *:80>
ServerName foo.com
ProxyPreserveHost On
ProxyPass / http://127.0.0.1:8080/
ProxyPassReverse / http://127.0.0.1:8080/
ProxyPass /api/ http://127.0.0.1:8081/
ProxyPassReverse /api/ http://127.0.0.1:8081/
</VirtualHost>
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solved Is it possible to have flask api running on apache with already running PHP site for same domain? [closed]