This page describes how to use worker tags and filters to control which workers are allowed to handle a given target. This can be used to control traffic locality. As an example, this can be used to ensure that traffic going into a public cloud is only handled by workers running within that same cloud.

»Worker Tags

Starting in Boundary 0.1.5, a worker can be configured with a set of key/value tags in its configuration file. The keys and values can be any lower-cased printable value. Each key can have more than one value:

worker {
  name = "web-prod-us-east-1"
  tags {
    region = ["us-east-1"]
    type   = ["prod", "webservers"]
  }
}

As HCL is JSON-compatible, this turns into an input JSON value of:

{
  "worker": {
    "name": "web-prod-us-east-1",
    "tags": {
      "region": ["us-east-1"],
      "type": ["prod", "webservers"]
    }
  }
}

Note that this is the canonical format, as it maps closely to the filter structure. However, for compatibility with some other systems, it is also possible to specify the tags in a pure key=value style:

worker {
  name = "web-prod-us-east-1"
  tags = ["region=us-east-1", "type=prod", "type=webservers"]
}

In this format, it is not possible to have an equal sign be a part of the key.

»Target Worker Filtering

Once workers have tags, it is possible to use these tags to control which workers are allowed to handle a given session by specifying a worker_filter attribute when configuring targets.

As filters operate on JSON Pointer selectors, the values that are input into the filter come from the JSON representation of the values in the configuration file nested under tags and include a name value:

{
  "name": "web-prod-us-east-1",
  "tags": {
    "region": ["us-east-1"],
    "type": ["prod", "webservers"]
  }
}

If an expression fails due to a key not being found within the input data, the worker is not included in the final set, so ensure that all workers that should match a given filter are populated with tags referenced in the filter string. As a corollary, it is not possible to distinguish between a worker that is not included due to the expression itself and a worker that did not have correct tags.

Following are some examples of using these values in filters:

Name regex: "/name" matches "web-prod-us-east-[12]", which would match workers whose names are web-prod-us-east-1 or web-prod-us-east-2
Region: "us-east-1" in "/tags/region". Note that each tag can have multiple values, so it must use the in operator to search in the collection. If you know that you have only one value, an equivalent would be "/tags/region/0" == "us-east-1".
Grouping: ("us-east-1" in "/tags/region" and "/name" == "web-prod-us-east-1") or "webservers" in "/tags/type"