k8sUtils
Introduction
A set of pods, deployments interacting with a kubernetes installation.
Inheritance
Configurations need to support a form of inheritance so that each configuration can be modified independently. Within k8sUtils we borrow the concepts of inclusion and inheritance through composition. For example `haskell For example, DiscourseConfiguration includes CommonConfiguration to use commonly defined labels, registry.
` This approach does have its disadvantages and something we will revisit.
Some conventions
We like to flatten hierarchies unless needed. For example,
haskell module CommonTypes where ...
is preferable to
haskell module Data.CommonTypes where ...
We may still need to maintain Internal modules to layer the interface; so much for convention.
Design approach
The pods rely on microlens as the client libraries provide code for these lenses. Yes we all feel the churn every time the installation compiles for the first time.
A brief introduction to microlens for k8s
Let us take the following example,
apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
name: nginx-deployment
spec:
selector:
matchLabels:
app: nginx
replicas: 2 # tells deployment to run 2 pods matching the template
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:1.7.9
ports:
- containerPort: 80
The corresponding version in haskell.The size of the function is almost the same size as the configuration file, with added functions for lenses, that we are not showing below.
makeDeployment :: NginxParameters -> V1Deployment
makeDeployment nginxParams =
mkV1Deployment &
v1DeploymentMetadataL .~ (Just mkV1ObjectMeta) &
v1DeploymentMetadataL . _Just . v1ObjectMetaNameL .~ (Just . coerce $ nginxParams ^. metadataName) &
v1DeploymentApiVersionL .~ (Just . coerce $ nginxParams ^. DeploymentParameters.apiVersion) &
v1DeploymentKindL .~ (Just "deployment") &
v1DeploymentSpecL .~ (Just $ mkV1DeploymentSpec mkV1LabelSelector mkV1PodTemplateSpec) &
v1DeploymentSpecL . _Just . v1DeploymentSpecSelectorL . v1LabelSelectorMatchLabelsL .~ (Just $ fromList [("app", coerce $ nginxParams ^. appName)]) &
v1DeploymentSpecL . _Just . v1DeploymentSpecReplicasL .~ (Just . naturalToInt . coerce $ nginxParams ^. replicas) &
v1DeploymentSpecL . _Just . v1DeploymentSpecTemplateL . v1PodTemplateSpecSpecL .~ (Just $ mkV1PodSpec [mkV1Container "nginx"]) &
v1DeploymentSpecL . _Just . v1DeploymentSpecTemplateL . v1PodTemplateSpecSpecL . _Just . v1PodSpecContainersL .~
[
mkV1Container "nginx" &
v1ContainerNameL .~ (coerce $ nginxParams ^. appName) &
v1ContainerPortsL .~ (Just [mkV1ContainerPort $ naturalToInt . coerce $ nginxParams ^. containerPort]) &
v1ContainerImageL .~ (Just $ coerce $ nginxParams ^. deploymentImage)
]
Notes
The code could be much simpler if we allowed for the entire lens machinery in this library. A lot of microlens boilerplate can be reduced. We are going to decide to using microlens till we really get tired of writing these boilerplate lens functions or perhaps write a generator that we can use.