Conditions
The information on this page is written for Vamp v0.9.4
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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:
| description | syntax | example |
|---|---|---|
| match user agent | user-agent == value |
user-agent == Firefox |
| mismatch user agent | user-agent != value |
user-agent != Firefox |
| match host | host == value |
host == localhost |
| mismatch host | host != value |
host != localhost |
| has cookie | has cookie value |
has cookie vamp |
| misses cookie | misses cookie value |
misses cookie vamp |
| has header | has header value |
has header ETag |
| misses header | misses header value |
misses header ETag |
| match cookie value | cookie name has value |
cookie vamp has 12345 |
| mismatch cookie value | cookie name misses value |
cookie vamp misses 12345 |
| header has value | header name has value |
header vamp has 12345 |
| header misses value | header name misses value |
header vamp misses 12345 |
- 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.
What next?
- Read about Vamp dialects
- Check the API documentation
- Try Vamp
Last updated on September 7, 2018
