It looks like ext-rdkafka is going to be the future standard, but is currently in alpha and cannot be used without packaging. Try to find another library that stays close to the librdkafka bindings, to make future migration simpler.
== Leading candidate
https://github.com/arnaud-lb/php-rdkafka
Supports Kafka 0.8 and 0.9, designed as a thin binding layer above librdkafka. This is the only Kafka extension to make it into PECL.
== Other candidates
nmred/kafka-php -> We've chopped the consumer bits out and made some big changes, so the WMF fork is not suitable for this project. It seems to be PHP-only, which makes it a good fallback if packaging turns out to be difficult.
https://github.com/hauptmedia/php-rdkafka -> Wrapper around ext-rdkafka, which might be nice in the future. Only one contributor so far.