I'll assume that you're asking out of a genuine curiosity born from a lack of knowledge of either system and not a question of "why was this made?"

Hadoop is a computing ecosystem. The Hadoop project is not only a computing framework, but it's a datacenter work scheduler (YARN), a distributed filesystem (HDFS), computing framework (MapReduce), HBase (database built on top of HDFS) and a whole host of other complimentary technologies. Admittedly, when most people say "Hadoop", they refer to MapReduce. MapReduce is a batch computation framework principally for executing filtering or aggregation over large amounts of data (e.g. finding top referrers from request logs).

InfluxDB is a distributed timeseries database. The closest analogue in the Hadoop ecosystem would be HBase running OpenTSDB. InfluxDB is aiming to fill the niche of high-volume metric collection and analysis. A system like InfluxDB (or any other time-series storage solution) aims to observe data over time for use in dashboarding, alerting, and general analysis over time. For example, tracking pageviews per second or response times.

I encourage you to take a look at all these projects, they're fantastic when you need them.