ecs

ECS Tooling Usage

In addition to the published schema and artifacts, the ECS repo also contains tools to generate artifacts based on the current published and custom schemas.

You may be asking if ECS is a specification for storing event data, where does the ECS tooling fit into the picture? As users implement ECS into their Elastic stack, common questions arise:

• ECS has too many fields. Users don’t want to generate mappings for fields they don’t plan on using soon.
• Users want to adopt ECS but also want to painlessly maintain their own custom field mappings alongside ECS.

Users can use the ECS tools to tackle both problems. What artifacts are relevant will also vary based on need. Many users will find the Elasticsearch templates most useful, but Beats contributors will instead find the Beats-formatted YAML field definition files valuable. By maintaining only their customizations and use the tools provided by ECS, they can generate relevant artifacts for their unique set of data sources.

NOTE - These tools and their functionality are considered experimental.

Table of Contents

• TLDR Example
• Terminology
• Setup and Install
  • Prerequisites
    • Clone from GitHub
    • Install dependencies
• Usage
  • Getting Started - Generating Artifacts
  • Generator Options
    • Out
    • Include
    • Exclude
    • Subset
    • Ref
    • Mapping & Template Settings
    • Strict Mode
    • Intermediate-Only
    • Force-docs

TLDR Example

Before diving into the details, here’s a complete example that:

• takes ECS 1.6 fields
• selects only the subset of fields relevant to the project’s use case
• includes custom fields relevant to the project
• outputs the resulting artifacts to a project directory
• replace the ECS project’s sample template settings and mapping settings with ones appropriate to the project

python scripts/generator.py --ref v1.6.0 \
  --subset            ../my-project/fields/subset.yml \
  --include           ../my-project/fields/custom/ \
  --out               ../my-project/ \
  --template-settings-legacy ../my-project/fields/template-settings-legacy.json \
  --template-settings ../my-project/fields/template-settings.json \
  --mapping-settings  ../my-project/fields/mapping-settings.json

The generated Elasticsearch template would be output at

my-project/generated/elasticsearch/legacy/template.json

If this sounds interesting, read on to learn all about each of these settings.

See usage-example/ for a complete example with source files.

Terminology

Term	Definition
ECS	Elastic Common Schema. For the purposes of this guide, ECS may refer to either the schema itself or the repo/tooling used to maintain the schema
artifacts	Various kinds of files or programs that can be generated based on ECS
field set	Groups of related fields in ECS
schema	Another term for a group of related fields in ECS. Used interchangeably with field set
schema definition	The markup used to define a schema in ECS
attributes	The properties of a field or field set that are used to define that field or field set in a schema definition

Setup and Install

Prerequisites

• Python 3.8+
• make
• pip
• git

Clone from GitHub

The recommended way to download the ECS repo is git clone:

$ git clone https://github.com/elastic/ecs
$ cd ecs

Prior to installing dependencies or running the tools, it’s recommended to check out the git branch for the ECS version being targeted.

Example: For ECS 1.5.0:

$ git checkout v1.5.0

Install dependencies

Install dependencies using pip (An active virtualenv is recommended):

$ pip install -r scripts/requirements.txt

Usage

Getting Started - Generating Artifacts

Using the defaults, the generator script generates the artifacts based on the current ECS schema.

$ python scripts/generator.py
Loading schemas from local files
Running generator. ECS version 1.5.0

Points to note on the defaults:

• Artifacts are created in the generated directory and the entire schema is included
• Documentation updates will be written to the appropriate file under the docs directory. More specifics on generated doc files is covered in the contributor’s file
• Each run of the script will rewrite the entirety of the generated directory
• The script will need to be executed from the top-level of the ECS repo
• The version displayed when running generator.py is based on the current value of the version file in the top-level of the repo

The generator’s defaults are how the ECS team maintains the official artifacts published in the repo. For your own use cases, you may wish to add your own fields or remove others that are unused. The following section details the available options for controlling the output of those artifacts.

Generator Options

Out

Generate the ECS artifacts in a different output directory. If the specified directory doesn’t exist, it will be created:

$ python scripts/generator.py --out ../myproject/ecs/out/

Inside the directory passed in as the target dir to the --out flag, two directories, generated and docs, will be created. docs will contain three asciidoc files based on the contents of the provided schema. generated will contain the various artifacts laid out as in the published repo (beats, csv, ecs, elasticsearch).

Note: When running using either the --subset or --include options, the asciidoc files will not be generated.

Include

Use the --include flag to generate ECS artifacts based on the current ECS schema field definitions plus provided custom fields:

$ python scripts/generator.py --include ../myproject/ecs/custom-fields/
$ python scripts/generator.py --include ../myproject/ecs/custom-fields/ ../myproject/ecs/more-custom-fields/
$ python scripts/generator.py --include ../myproject/ecs/custom-fields/myprefix*.yml
$ python scripts/generator.py --include ../myproject/ecs/custom-fields/[some]*[re].yml
$ python scripts/generator.py --include ../myproject/ecs/custom-fields/myfile1.yml ../myproject/ecs/custom-fields/myfile2.yml

The --include flag expects one or more directories or subsets of schema YAML files using the same file format as the ECS schema files. This is useful for maintaining custom field definitions that are outside of the ECS schema, but allows for merging the custom fields with the official ECS fields for your deployment.

For example, if we defined the following schema definition in a file named myproject/ecs/custom-fields/widget.yml:

---
- name: widgets
  title: Widgets
  group: 2
  short: Fields describing widgets
  description: >
    The widget fields describe a widget and all its widget-related details.
  type: group
  fields:

    - name: id
      level: extended
      type: keyword
      short: Unique identifier of the widget
      description: >
        Unique identifier of the widget.

Multiple directory targets can also be provided:

$ python scripts/generator.py \
    --include ../myproject/custom-fields-A/  ../myproject/custom-fields-B \
    --out ../myproject/out/

Generate artifacts using --include to load our custom definitions in addition to --out to place them in the desired output directory:

$ python scripts/generator.py --include ../myproject/custom-fields/ --out ../myproject/out/
Loading schemas from local files
Running generator. ECS version 1.5.0
Loading user defined schemas: ['../myproject/custom-fields/']

We see the artifacts were generated successfully:

$ ls -lah ../myproject/out/
total 0
drwxr-xr-x  2 user  ecs    64B Jul  8 13:12 docs
drwxr-xr-x  6 user  ecs   192B Jul  8 13:12 generated

And looking at a specific artifact, ../myprojects/out/generated/elasticsearch/legacy/template.json, we see our custom fields are included:

...
      "widgets": {
        "properties": {
          "id": {
            "ignore_above": 1024,
            "type": "keyword"
          }
        }
      }
...

Include can be used together with the --ref flag to merge custom fields into a targeted ECS version. See Ref.

NOTE: The --include mechanism will not validate custom YAML files prior to merging. This allows for modifying existing ECS fields in a custom schema without having to redefine all the mandatory field attributes.

Exclude

Use the --exclude flag to generate ephemeral ECS artifacts based on the current ECS schema field definitions minus fields considered for removal, e.g. to assess impact of removing these. Warning! This is not the recommended route to remove a field permanently as it is not intended to be invoked during the build process. Definitive field removal should be implemented using a custom Subset or via the RFC process. Example:

$ python scripts/generator.py --exclude ../myproject/ecs/custom-fields/
$ python scripts/generator.py --exclude ../myproject/ecs/custom-fields/ ../myproject/ecs/more-custom-fields/
$ python scripts/generator.py --exclude ../myproject/ecs/custom-fields/myprefix*.yml
$ python scripts/generator.py --exclude ../myproject/ecs/custom-fields/[some]*[re].yml
$ python scripts/generator.py --exclude ../myproject/ecs/custom-fields/myfile1.yml ../myproject/ecs/custom-fields/myfile2.yml

The --exclude flag expects one or more directories or subsets of schema YAML files using the same file format as the ECS schema files. You can also use a subset, provided that relevant name and fields fields are preserved.

---
- name: log
  fields:
    - name: original

The root Field Set name must always be present and specified with no dots .. Subfields may be specified using dot notation, for example:

---
- name: log
  fields:
    - name: syslog.severity.name

Generate artifacts using --exclude to load our custom definitions in addition to --out to place them in the desired output directory:

$ python scripts/generator.py --exclude ../myproject/exclude-set.yml/ --out ../myproject/out/
Loading schemas from local files
Running generator. ECS version 1.11.0

Subset

If your indices will never populate particular ECS fields, there’s no need to include those field definitions in your index mappings, with the exception of the base fieldset, which must exist and which must contain at least the @timestamp field. The --subset argument allows for passing a subset definition YAML file which indicates which field sets or specific fields to include in the generated artifacts.

$ python scripts/generator.py --subset ../myproject/ecs/subset-fields/
$ python scripts/generator.py --subset ../myproject/ecs/subset-fields/ ../myproject/ecs/more-subset-fields/
$ python scripts/generator.py --subset ../myproject/ecs/custom-fields/subset.yml
$ python scripts/generator.py --subset ../myproject/ecs/custom-fields/[some]*[re].yml
$ python scripts/generator.py --subset ../myproject/ecs/custom-fields/myfile1.yml ../myproject/ecs/custom-fields/myfile2.yml

Example subset file:

---
name: malware_event
fields:
  base:
    fields:
      "@timestamp": {}
  agent:
    fields: "*"
  dll:
    fields: "*"
  ecs:
    fields: "*"
  process:
    fields:
      same_as_process:
        docs_only: True

The subset file has a defined format, starting with the two top-level required fields:

• name: The name of the subset. Also used to name the directory holding the generated subset intermediate files (e.g. <outputTarget>/generated/ecs/subset/<name>)
• fields Contains the subset field filters

The fields object declares which fields to include:

• The targeted field sets are declared underneath fields by their top-level name (e.g. base, agent, etc.)
• Underneath each field set, all sub-fields can be captured using a wildcard syntax: fields: "*"
• Individual leafs fields can also be targeted: @timestamp: {}
• For special cases, the docs_only: True attribute will add a field into ./docs but not add into any other generated artifact. The only current use case for this feature is to document fields only populated in reused field sets.

Reviewing the above example, the generator using subset will output artifacts containing:

• The @timestamp field from the base field set
• All agent.* fields, dll.*, and ecs.* fields

It’s also possible to combine --include and --subset together! Do note that your subset YAML filter file will need to list any custom fields being passed with --include. Otherwise, --subset will filter those fields out.

Example with --include and --subset file:

python scripts/generator.py --subset ./usage-example/fields/subset.yml --include ./usage-example/fields/custom/acme.yml

Ref

The --ref argument allows for passing a specific git tag (e.g. v1.5.0) or commit hash (1454f8b) that will be used to build ECS artifacts.

$ python scripts/generator.py --ref v1.5.0

The --ref argument loads field definitions from the specified git reference (branch, tag, etc.) from directories ./schemas and ./experimental/schemas (when specified via --include).

Here’s another example loading both ECS fields and experimental changes from branch “1.7”, then adds custom fields on top.

$ python scripts/generator.py --ref 1.7 --include experimental/schemas ../myproject/fields/custom --out ../myproject/out

The command above will produce artifacts based on:

• main ECS field definitions as of branch 1.7
• experimental ECS changes as of branch 1.7
• custom fields in ../myproject/fields/custom as they are on the filesystem

Note: --ref does have a dependency on git being installed and all expected commits/tags fetched from the ECS upstream repo. This will unlikely be an issue unless you downloaded the ECS as a zip archive from GitHub vs. cloning it.

Mapping & Template Settings

The --template-settings-legacy / --template-settings and --mapping-settings arguments allow overriding the default template and mapping settings, respectively, in the generated Elasticsearch template artifacts. Both artifacts expect a JSON file which contains custom settings defined.

$ python scripts/generator.py --template-settings-legacy ../myproject/es-overrides/template.json --mapping-settings ../myproject/es-overrides/mappings.json

The --template-settings-legacy argument defines index level settings that will be applied to the legacy index template in the generated artifacts. The --template-settings argument now defines those same settings, but for the composable template in the generated artifacts.

This is an example template.json to be passed with --template-setting-legacy:

{
  "index_patterns": ["mylog-*"],
  "order": 1,
  "settings": {
    "index": {
      "mapping": {
        "total_fields": {
          "limit": 10000
        }
      },
      "refresh_interval": "1s"
    }
  },
  "mappings": {}
}

--mapping-settings works in the same way except now with the mapping settings for the index. This is an example mapping.json file:

{
  "_meta": {
    "version": "1.5.0"
  },
    "date_detection": false,
    "dynamic_templates": [
      {
        "strings_as_keyword": {
          "mapping": {
            "ignore_above": 1024,
            "type": "keyword"
          },
          "match_mapping_type": "string"
        }
      }
    ],
    "properties": {}
}

For template.json, the mappings object is left empty: {}. Likewise the properties object remains empty in the mapping.json example. This will be filled in automatically by the script.

Strict Mode

The --strict argument enables “strict mode”. Strict mode performs a stricter validation step against the schema’s contents.

Basic usage:

$ python scripts/generator.py --strict

Strict mode requires the following conditions, else the script exits on an exception:

• Short descriptions must be less than or equal to 120 characters.
• Example values containing arrays or objects must be quoted to avoid unexpected YAML interpretation when the schema files or artifacts are relied on downstream.
• If a regex pattern is defined, the example values will be checked against it.
• If expected_values is defined, the example value(s) will be checked against the list.

The current artifacts generated and published in the ECS repo will always be created using strict mode. However, older ECS versions (pre v1.5.0) will cause an exception if attempting to generate them using --strict. This is due to schema validation checks introduced after that version was released.

Example:

$ python scripts/generator.py --ref v1.4.0 --strict
Loading schemas from git ref v1.4.0
Running generator. ECS version 1.4.0
...
ValueError: Short descriptions must be single line, and under 120 characters (current length: 134).
Offending field or field set: number
Short description:
  Unique number allocated to the autonomous system. The autonomous system number (ASN) uniquely identifies each network on the Internet.

Removing --strict will display a warning message, but the script will finish its run successfully:

$ python scripts/generator.py --ref v1.4.0
Loading schemas from git ref v1.4.0
Running generator. ECS version 1.4.0
/Users/ericbeahan/dev/ecs/scripts/generators/ecs_helpers.py:176: UserWarning: Short descriptions must be single line, and under 120 characters (current length: 134).
Offending field or field set: number
Short description:
  Unique number allocated to the autonomous system. The autonomous system number (ASN) uniquely identifies each network on the Internet.

This will cause an exception when running in strict mode.

Intermediate-Only

The --intermediate-only argument is used for debugging purposes. It only generates the “intermediate files”, ecs_flat.yml and ecs_nested.yml, without generating the rest of the artifacts. More information on the different intermediate files can be found in the generated directory’s README.

Force-docs

By default, running the generator with --subset, --include, or --exclude flags will not generate the ECS docs in the docs directory. Use --force-docs to force the documentation to generate even if one of those flags is also present.

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