Add Curator extension (#297)

extensions/curator/Dockerfile

+FROM alpine:3.8
+
+ENV CURATOR_VERSION=5.5.4
+
+RUN apk --update add --no-cache tini python py-pip \
+  && pip install elasticsearch-curator==${CURATOR_VERSION}
+
+COPY entrypoint.sh /
+
+WORKDIR /usr/share/curator
+COPY config ./config
+
+ENTRYPOINT ["/entrypoint.sh"]

extensions/curator/README.md

+# Curator
+
+Elasticsearch Curator helps you curate or manage your indices.
+
+## Usage
+
+If you want to include the Curator extension, run Docker Compose from the root of the repository with an additional
+command line argument referencing the `curator-compose.yml` file:
+
+```bash
+$ docker-compose -f docker-compose.yml -f extensions/curator/curator-compose.yml up
+```
+
+All configuration files are available in the `config/` directory.
+
+## Documentation
+
+https://github.com/elastic/curator

extensions/curator/config/curator.yml

+---
+# Remember, leave a key empty if there is no value. None will be a string,
+# not a Python "NoneType"
+client:
+  hosts:
+    - ${ELASTICSEARCH_HOST}
+  port: 9200
+  url_prefix:
+  use_ssl: False
+  certificate:
+  client_cert:
+  client_key:
+  aws_key:
+  aws_secret_key:
+  aws_region:
+  ssl_no_validate: False
+  http_auth:
+  timeout: 30
+  master_only: False
+
+logging:
+  loglevel: DEBUG
+  logfile:  /usr/share/curator/curator.log
+  logformat: default

extensions/curator/config/delete_log_files_curator.yml

+actions:
+  1:
+    action: delete_indices
+    description: >-
+      Delete indices. Find which to delete by first limiting the list to logstash-
+      prefixed indices. Then further filter those to prevent deletion of anything
+      less than ${UNIT_COUNT} days old. Ignore the error if the filter does not result in an
+      actionable list of indices (ignore_empty_list) and exit cleanly.
+    options:
+      ignore_empty_list: True
+      disable_action: False
+    filters:
+    - filtertype: pattern
+      kind: prefix
+      value: logstash-
+    - filtertype: age
+      source: creation_date
+      direction: older
+      unit: days
+      unit_count: ${UNIT_COUNT}

extensions/curator/curator-compose.yml

+version: '2'
+
+services:
+
+
+  curator:
+    build:
+      context: extensions/curator/
+    environment:
+      ELASTICSEARCH_HOST: elasticsearch
+      CRON: 0 0 * * *
+      CONFIG_FILE: /usr/share/curator/config/curator.yml
+      COMMAND: /usr/share/curator/config/delete_log_files_curator.yml
+      UNIT_COUNT: 2
+    networks:
+      - elk
+    depends_on:
+      - elasticsearch

extensions/curator/entrypoint.sh

+#!/bin/sh
+
+echo "$CRON /usr/bin/curator  --config ${CONFIG_FILE} ${COMMAND}" >>/etc/crontabs/root
+
+# https://github.com/krallin/tini/blob/master/README.md#subreaping
+tini -s -- crond -f -d 8 -l 8