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Adding label selector support to Corefile (#208)

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* Adding parsing for label selector to Corefile

* Updating comment typo in k8sCorefile

* Adding implementation of label support to filter exposed objects

* Updating TODO list
This commit is contained in:
Michael Richmond
2016-08-12 20:44:08 -07:00
committed by GitHub
parent 3b7b9b49d5
commit ad2838b916
6 changed files with 194 additions and 47 deletions
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31
middleware/kubernetes/README.md
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@@ -44,6 +44,13 @@ This is the default kubernetes setup, with everything specified in full:
template {service}.{namespace}.{zone}
# Only expose the k8s namespace "demo"
namespaces demo
# Only expose the records for kubernetes objects
# that matches this label selector. The label
# selector syntax is described in the kubernetes
# API documentation: http://kubernetes.io/docs/user-guide/labels/
# Example selector below only exposes objects tagged as
# "application=nginx" in the staging or qa environments.
#labels environment in (staging, qa),application=nginx
}
# Perform DNS response caching for the coredns.local zone
# Cache timeout is provided by the integer in seconds
@@ -51,10 +58,13 @@ This is the default kubernetes setup, with everything specified in full:
}
~~~
Notes:
Defaults:
* If the `namespaces` keyword is omitted, all kubernetes namespaces are exposed.
* If the `template` keyword is omitted, the default template of "{service}.{namespace}.{zone}" is used.
* If the `resyncperiod` keyword is omitted, the default resync period is 5 minutes.
* The `labels` keyword is only used when filtering of results based on kubernetes label selector syntax
is required. The label selector syntax is described in the kubernetes API documentation at:
http://kubernetes.io/docs/user-guide/labels/
### Basic Setup
@@ -191,7 +201,7 @@ mynginx.demo.coredns.local. 0 IN A 10.0.0.10
## Implementation Notes/Ideas
### Basic Zone Mapping (implemented)
### Basic Zone Mapping
The middleware is configured with a "zone" string. For
example: "zone = coredns.local".
@@ -200,8 +210,8 @@ to: "myservice.mynamespace.coredns.local".
The middleware should publish an A record for that service and a service record.
Initial implementation just performs the above simple mapping. Subsequent
revisions should allow different namespaces to be published under different zones.
If multiple zone names are specified, the records for kubernetes objects are
exposed in all listed zones.
For example:
@@ -262,11 +272,6 @@ return the IP addresses for all services with "nginx" in the service name.
TBD:
* How does this relate the the k8s load-balancer configuration?
* Do wildcards search across namespaces? (Yes)
* Initial implementation assumes that a namespace maps to the first DNS label
below the zone managed by the kubernetes middleware. This assumption may
need to be revised. (Template scheme for record names removes this assumption.)
## TODO
* SkyDNS compatibility/equivalency:
@@ -318,19 +323,19 @@ TBD:
* Additional features:
* Reverse IN-ADDR entries for services. (Is there any value in supporting
reverse lookup records?) (need tests, functionality should work based on @aledbf's code.)
* How to support label specification in Corefile to allow use of labels to
indicate zone? (Is this even useful?) For example, the following
* (done) ~~How to support label specification in Corefile to allow use of labels to
indicate zone? For example, the following
configuration exposes all services labeled for the "staging" environment
and tenant "customerB" in the zone "customerB.stage.local":
kubernetes customerB.stage.local {
# Use url for k8s API endpoint
endpoint http://localhost:8080
label "environment" : "staging", "tenant" : "customerB"
labels environment in (staging),tenant=customerB
}
Note: label specification/selection is a killer feature for segmenting
test vs staging vs prod environments.
test vs staging vs prod environments.~~ Need label testing.
* Implement IP selection and ordering (internal/external). Related to
wildcards and SkyDNS use of CNAMES.
* Flatten service and namespace names to valid DNS characters. (service names