[alpine images] Coolio::StatWatcher fallbacks to polling instead of using inotify

[adw1n]

Description

When I use the fluent/fluentd:v1.1.0 image the in_tail plugin fallbacks to polling file every 5 seconds instead of using inotify. This causes loss in timestamp precision. fluent/fluentd:v1.1.0-debian image handles watching file correctly and does not fallback to polling.

Steps to reproduce

1. put Dockerfile, fluent.conf and write_logs.sh in one directory Dockerfile

   
   FROM fluent/fluentd:v1.1.0

COPY ./fluent.conf /fluentd/etc/fluent.conf COPY ./write_logs.sh /usr/local/bin/write-logs RUN chmod 755 /usr/local/bin/write-logs

RUN find . -name in_tail.rb | xargs sed -i '/line.chomp!/a \ \ \ \ \ \ \ \ puts Time.now.to_datetime.iso8601(3)'

fluent.conf

@type tail path /tmp/test.log pos_file /tmp/test.log.pos tag test path_key tailed_test keep_time_key true format none enable_watch_timer false

write_logs.sh

!/bin/sh

counter=0 while true; do sleep 0.01 echo $counter >> /tmp/test.log counter=expr $counter + 1 done

2. run `docker build -t inotify_problem . && docker run --name inotify_problem -it inotify_problem`
3. run `docker exec -it inotify_problem write-logs`

As you can see, logs are being polled with 5 sec frequency (`convert_line_to_event` function is executed every ~5 sec).

Now change `fluent/fluentd:v1.1.0` to `fluent/fluentd:v1.1.0-debian` in the Dockerfile and run:
1. `docker stop inotify_problem; docker rm inotify_problem; docker rmi inotify_problem`
2. `docker build -t inotify_problem . && docker run --name inotify_problem -it inotify_problem`
3. `docker exec -it inotify_problem write-logs`

Observe that `convert_line_to_event` function is executed every ~0.01 sec.

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