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Conventions

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Conventions

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The implementation of ECS follows a few conventions. Understanding them will help you understand ECS better.

Datatype for integers

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Unless otherwise noted, the datatype used for integer fields should be long.

IDs and most codes are keywords, not integers

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Despite the fact that IDs and codes (such as error codes) are often integers, this is not always the case. Since we want to make it possible to map as many systems and data sources to ECS as possible, we default to using the keyword type for IDs and codes.

Some specific kinds of codes are always integers, like HTTP status codes. If those have a specific corresponding specific field (as HTTP status does), its type can safely be an integer type. But generic fields like error.code cannot have this guarantee, and are therefore keyword.

Text indexing and multi-fields

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Elasticsearch can index text using datatypes:

text Text indexing allows for full text search, or searching arbitrary words that are part of the field. See Text datatype in the Elasticsearch Reference Guide.
keyword Keyword indexing offers faster exact match filtering, prefix search (like autocomplete), and makes aggregations (like Kibana visualizations) possible. See the Elasticsearch Reference Guide for more information on exact match filtering, prefix search, or aggregations.

Default Elasticsearch convention for indexing text fields

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Unless your index mapping or index template specifies otherwise (as the ECS index template does), Elasticsearch indexes a text field as text at the canonical field name, and indexes a second time as keyword, nested in a multi-field.

Default Elasticsearch convention:

Canonical field: myfield is text
Multi-field: myfield.keyword is keyword

ECS convention for indexing text fields

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ECS flips the above convention around.

For monitoring use cases, keyword indexing is needed almost exclusively, with full text search needed on very few fields. Moreover, indexing for full text search on lots of fields, where it’s not expected to be used is wasteful of resources.

Given these two premises, ECS defaults all text indexing to keyword datatype (with very few exceptions). Any use case that requires full text search indexing on additional fields can add a multi-field for full text search. Doing so does not conflict with ECS, as the canonical field name will remain keyword indexed.

So the ECS multi-field convention for text is:

Canonical field: myfield is keyword
Multi-field: myfield.text is text

Exceptions

The only exceptions to this convention are fields message and error.message, which are indexed for full text search only, with no multi-field. These two fields don’t follow the new convention because they are deemed too big of a breaking change with these two widely used fields in Beats.

Any future field that will be indexed for full text search in ECS will however follow the multi-field convention where text indexing is nested in the multi-field.

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