- Elasticsearch – The _cat APIs and Reading Cluster Health
The APIs you actually type when something is wrong. _cat/health, indices, nodes, shards and allocation, with the v, h and s parameters that make them readable. Then the questions they answer: what yellow really means and why a single-node cluster is yellow by default, which shard is unassigned and why, where the disk went, and how to tell a slow query from a slow cluster.
- Linux Screen
Imagine having to execute a long running process and waiting for it to finish, most likely you are connected via ssh and you can’t do anything else but waiting for that process to finish. When the process is taking too long your connection will time out and you will be kicked out. When that happens…
- Elasticsearch – Aliases and Zero-Downtime Reindexing
A field type cannot be changed once it has been written, so sooner or later you have to move every document into a new index. Whether that is an outage depends on one decision you make on day one: never let your application name a concrete index. Aliases, _reindex, the atomic alias swap, what happens to writes that land during the copy, and how to migrate a cluster that already got this wrong.
- Elasticsearch – Geo Queries and geo_point
“Show me places near here”, done properly. Mapping geo_point and the five formats it accepts — including the one that reverses longitude and latitude and silently puts your listings in the Gulf of Guinea. geo_distance as a filter, geo_bounding_box for a map viewport, sorting by _geo_distance and reading the distance back off each hit for free, and geo_shape when a point is not enough.
- Elasticsearch – Aggregations and Faceted Search
Aggregations are the other half of Elasticsearch, and the half that turns a search box into a filter panel. Metric, bucket and pipeline aggregations, nesting them, aggregating on keyword rather than text and why that is not optional, and the part most tutorials skip: a facet counted inside its own filter collapses to a single row, so the guest can never switch cities without clearing the filter first.