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+This is an example how Elasticsearch can be synchronized with a MySQL database by using Logstash.
+
+# How it works
+The MySQL database stores `articles` in a table and every time an article gets inserted or updated, Logstash takes care 
+of that the changes are synchronized to Elasticsearch.
+
+![component-diagram](https://www.plantuml.com/plantuml/img/SoWkIImgAStDuUAAzgqC3lI9vVBCAqajIajCJbNmSd5ovehsoKy7AYhEYEMATir9B2x9J2vEJInApa1MwH4I4i351LEfe9kINvwdgm4n04CKh1XicO9kQO4kH1MAqH1nYA4EgNafGFS10000)
+
+To keep them in sync, Logstash polls the MySQL instance every 5 seconds and checks the articles table for updates. 
+The articles table has a `modifcation_time` column and Logstash tracks the last known value to query the updates (see 
+[sync-pipeline.conf](logstash/sync-pipeline.conf)).
+
+# Prerequisites
+* `docker` and `docker-compose`
+
+# Getting started
+1. Execute `docker-compose up` to startup all components (MySQL, Elasticsearch and Logstash). 
+1. Connect to the MySQL database and insert some articles (schema: `blog`, username: `blog`, password: `blog`).
+    ```
+    insert into articles (id, title, content) values ('1','first_title','first_content');
+    insert into articles (id, title, content) values ('2','second_title','second_content');
+    insert into articles (id, title, content) values ('3','third_title','third_content');
+    ```
+1. Query Elasticsearch and see the result.
+   ```
+   curl localhost:9200/articles/_search
+   ```
+1. Insert and update some articles in MySQL and query Elasticsearch afterwards to see the changes.
+
+# Pitfalls
+* deleted articles in MySQL are still available in Elasticsearch
+* Logstash needs a JDBC driver to connect to the database
+
+# Implementation details
+* [docker-compose.yml](docker-compose.yml) starts the example
+* [sync-pipeline.conf](logstash/sync-pipeline.conf) contains the Logstash pipeline config
+* [schema.sql](mysql/schema.sql) defines the database schema
+
+# Further readings
+* https://www.elastic.co/blog/how-to-keep-elasticsearch-synchronized-with-a-relational-database-using-logstash