Conditions

Conditions are used by gateways to filter incoming traffic for routing between services in a cluster. Read more about gateway usage. You can define conditions inline in a blueprint or store them separately under a unique name on the /conditions endpoint and just use that name to reference them from a blueprint.

Example - simple inline condition

This would be used directly inside a blueprint.

---
condition_strength: 10%  # Amount of traffic for this service in percents.
condition: User-Agent = IOS

Create a condition

Creating conditions is quite easy. Checking Headers, Cookies, Hosts etc. is all possible. Under the hood, Vamp uses Haproxy’s ACL’s (cbonte.github.io/haproxy-dconv - 7.1 ACL basics) and you can use the exact ACL definition right in the blueprint in the condition field of a condition.

However, ACL’s can be somewhat opaque and cryptic. That’s why Vamp has a set of convenient “short codes” to address common use cases. Currently, we support the following:

• Additional syntax examples: github.com/magneticio/vamp - ConditionDefinitionParserSpec.scala.

Vamp is also quite flexible when it comes to the exact syntax. This means the following are all equivalent:

In order to specify plain HAProxy ACL, ACL needs to be between { }:

condition: "< hdr_sub(user-agent) Chrome >"

Having multiple conditions in a condition is perfectly possible. For example, the following condition would first check whether the string “Chrome” exists in the User-Agent header of a request and then it would check whether the request has the header “X-VAMP-MY-COOL-HEADER”. So any request matching both conditions would go to this service.

---
gateways:
  weight: 100%
  condition: "User-Agent = Chrome AND Has Header X-VAMP-MY-COOL-HEADER"

Using a tool like httpie (github.com/jkbrzt/httpie) makes testing this a breeze.

http GET http://10.26.184.254:9050/ X-VAMP-MY-COOL-HEADER:stuff

Boolean expression in conditions

Vamp supports AND, OR, negation NOT and grouping ( ):

---
gateways:
  weight: 100%
  condition: (User-Agent = Chrome OR User-Agent = Firefox) AND has cookie vamp

• Additional boolean expression examples: github.com/magneticio/vamp - BooleanParserSpec.scala.