PHP Warning: PHP Startup: Unable to load dynamic library \'/usr/lib/php/20151012/mongodb.so\' - /usr/lib/php/20151012/mongodb.so: undefined symbol: php_json_
I think the problem is here that mongodb.so depends on json.so. The solution is to load mongodb.so after json.so.
I guess you are using the custom Mongo script for Homestead. The script outputs the mongodb.so module in php.ini file with the result that mongodb.so is loaded first. You should create a mongodb.ini file where mongodb.so is loaded.
Create the .ini-file: /etc/php/7.0/mods-available/mongodb.ini with content:
; configuration for php mongo module
; priority=30
extension=mongodb.so
Give it priority 30, since json gets 20 (in my settings) to be sure it is loaded afterwards.
Create a softlink of the ini-file to /etc/php/7.0/fpm/conf.d to make it available for the webserver.
ln -s /etc/php/7.0/mods-available/mongodb.ini 30-mongodb.ini
Reload webserver and php-fpm.
sudo service [your webserver] restart && sudo service php7.0-fpm restart
You are done! You can config the cli-version the same way