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SpecsUpdate
Pros
Pro Has an official Docker image
There is an official Docker image for Logstash which means it'll likely be well supported and maintained for a while.
Pro Extended functionality via plugins
There is a rich repository of plugins available categorized as inputs, codecs, filters and outputs.
Pro Easy installation
No dependencies, it's a single .jar file. It's written in JRuby and only requires Java to be installed.
Pro Great integration with other Elastic products
Logstash is commonly used as part of ELK stack, that also includes ElasticSearch (a clustered search and storage system) and Kibana (a web frontend for ElasticSearch).
Pro Filters are code
Filters, also known as "groks", are used to query a log stream. They are provided in a configuration file, that also configures source stream and output streams. Since they are stored in a file, they can be under version control and changes can be reviewed (for example, as part of a Git pull request).