Generate Dhall schemas for multiple Kubernetes versions (#104)

Fixes #75

This also changes the default version to the latest version to 1.17 since now
users can access older versions

Author: Gabriella439

1.12/README.md

@@ -0,0 +1,357 @@
+# `dhall-kubernetes`
+
+<img src="logo/dhall-kubernetes-logo.svg" alt="dhall-kubernetes logo" height="300px"/>
+
+`dhall-kubernetes` contains [Dhall][dhall-lang] bindings to [Kubernetes][kubernetes],
+so you can generate Kubernetes objects definitions from Dhall expressions.
+This will let you easily typecheck, template and modularize your Kubernetes definitions.
+
+## Why do I need this
+
+Once you build a slightly non-trivial Kubernetes setup, with many objects floating
+around, you'll encounter several issues:
+1. Writing the definitions in YAML is really verbose, and the actually important
+  things don't stand out that much
+2. Ok I have a bunch of objects that'll need to be configured together, how do I share data?
+3. I'd like to reuse an object for different environments, but I cannot make it parametric..
+4. In general, I'd really love to reuse parts of some definitions in other definitions
+5. Oh no, I typoed a key and I had to wait until I pushed to the cluster to get an error back :(
+
+The natural tendency is to reach for a templating language + a programming language to orchestrate that + some more configuration for it...
+But this is just really messy (been there), and we can do better.
+
+Dhall solves all of this, being a programming language with builtin templating,
+all while being non-Turing complete, strongly typed and [strongly normalizing][normalization]
+(i.e.: reduces everything to a normal form, no matter how much abstraction you build),
+so saving you from the *"oh-noes-I-made-my-config-in-code-and-now-its-too-abstract"* nightmare.
+
+For a Dhall Tutorial, see [the website][dhall-website], or the [readme of the project][dhall-lang],
+or the [full tutorial][dhall-tutorial].
+
+## Prerequisites
+
+**NOTE**: `dhall-kubernetes` requires at least version `1.27.0` of [the interpreter](https://github.com/dhall-lang/dhall-haskell)
+(version `11.0.0` of the language).
+
+## Quickstart - a simple Deployment
+
+Let's say we'd like to configure a Deployment exposing an `nginx` webserver.
+
+In the following example, we:
+1. Import the Kubernetes definitions as a Dhall package (the `package.dhall` file) from the local repo.
+   In your case you will want to replace the local path with a remote one, e.g.
+   `https://raw.githubusercontent.com/dhall-lang/dhall-kubernetes/master/package.dhall`
+   Note: the `sha256:..` is applied to some imports so that:
+     1. the import is cached locally after the first evaluation, with great time savings (and avoiding network calls)
+     2. prevent execution if the content of the file changes. This is a security feature, and you
+        can read more [in Dhall's "Security Guarantees" document][security-hashes]
+   Note: instead of using the `package.dhall` from the `master` branch, you may want to use a tagged release,
+     as the contents of the `master` branch are liable to change without warning.
+2. Define the [Deployment][deployment] using the schema pattern and hardcoding the deployment details:
+
+```dhall
+-- examples/deploymentSimple.dhall
+
+let kubernetes =
+      ../package.dhall sha256:ab1c971ddeb178c1cfc5e749b211b4fe6fdb6fa1b68b10de62aeb543efcd60b3
+
+let deployment =
+      kubernetes.Deployment::{
+      , metadata = kubernetes.ObjectMeta::{ name = "nginx" }
+      , spec =
+          Some
+            kubernetes.DeploymentSpec::{
+            , replicas = Some 2
+            , template =
+                kubernetes.PodTemplateSpec::{
+                , metadata = kubernetes.ObjectMeta::{ name = "nginx" }
+                , spec =
+                    Some
+                      kubernetes.PodSpec::{
+                      , containers =
+                          [ kubernetes.Container::{
+                            , name = "nginx"
+                            , image = Some "nginx:1.15.3"
+                            , ports =
+                                [ kubernetes.ContainerPort::{
+                                  , containerPort = 80
+                                  }
+                                ]
+                            }
+                          ]
+                      }
+                }
+            }
+      }
+
+in  deployment
+
+```
+
+We then run this through `dhall-to-yaml` to generate our Kubernetes definition:
+
+```bash
+dhall-to-yaml --omitEmpty < examples/deploymentSimple.dhall
+```
+
+And we get:
+```yaml
+## examples/out/deploymentSimple.yaml
+
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: nginx
+spec:
+  replicas: 2
+  template:
+    metadata:
+      name: nginx
+    spec:
+      containers:
+        - image: nginx:1.15.3
+          name: nginx
+          ports:
+            - containerPort: 80
+
+```
+
+## More modular: defining an Ingress
+
+The above is cool, but hardcoding data is not that cool.
+
+So in a more realistic deployment you'll probably want to define:
+- some `MyService` type that contains the config settings relevant to your deployments
+- some functions parametrized by this type, so that you can produce objects to send to k8s
+  by just applying these functions to `MyService` objects
+
+This is useful because then you can define your `Service`s separately from the Kubernetes logic,
+and reuse those objects for configuring other things (e.g. configuring the services themselves, 
+templating documentation, configuring Terraform deployments, you name it).
+
+As an example of that, next we'll define an Ingress (an [Nginx Ingress][nginx-ingress] in this case),
+containing stuff like TLS certs and routes for every service - see the [schema][Ingress].
+
+Things to note in the following example:
+- we define the `Service` type inline in the file, but in your case you'll want to have a
+  separate `./Service.dhall` file (so you can share around the project)
+- we define functions to create the TLS definitions and the routes, so that we can `map`
+  them over the list of services.
+- we also defined the list of `services` inline, but you should instead return the
+  `mkIngress` function instead of applying it, so you can do something like
+  `dhall-to-yaml --omitEmpty <<< "./mkIngress.dhall ./myServices.dhall"`
+
+```dhall
+-- examples/ingress.dhall
+
+let Prelude =
+      ../Prelude.dhall sha256:771c7131fc87e13eb18f770a27c59f9418879f7e230ba2a50e46f4461f43ec69
+
+let map = Prelude.List.map
+
+let kv = Prelude.JSON.keyText
+
+let kubernetes =
+      ../package.dhall sha256:ab1c971ddeb178c1cfc5e749b211b4fe6fdb6fa1b68b10de62aeb543efcd60b3
+
+let Service = { name : Text, host : Text, version : Text }
+
+let services = [ { name = "foo", host = "foo.example.com", version = "2.3" } ]
+
+let makeTLS
+    : Service → kubernetes.IngressTLS.Type
+    =   λ(service : Service)
+      → { hosts = [ service.host ]
+        , secretName = Some "${service.name}-certificate"
+        }
+
+let makeRule
+    : Service → kubernetes.IngressRule.Type
+    =   λ(service : Service)
+      → { host = Some service.host
+        , http =
+            Some
+              { paths =
+                  [ { backend =
+                        { serviceName = service.name
+                        , servicePort = kubernetes.IntOrString.Int 80
+                        }
+                    , path = None Text
+                    }
+                  ]
+              }
+        }
+
+let mkIngress
+    : List Service → kubernetes.Ingress.Type
+    =   λ(inputServices : List Service)
+      → let annotations =
+              [ kv "kubernetes.io/ingress.class" "nginx"
+              , kv "kubernetes.io/ingress.allow-http" "false"
+              ]
+        
+        let defaultService =
+              { name = "default"
+              , host = "default.example.com"
+              , version = " 1.0"
+              }
+        
+        let ingressServices = inputServices # [ defaultService ]
+        
+        let spec =
+              kubernetes.IngressSpec::{
+              , tls =
+                  map Service kubernetes.IngressTLS.Type makeTLS ingressServices
+              , rules =
+                  map
+                    Service
+                    kubernetes.IngressRule.Type
+                    makeRule
+                    ingressServices
+              }
+        
+        in  kubernetes.Ingress::{
+            , metadata =
+                kubernetes.ObjectMeta::{
+                , name = "nginx"
+                , annotations = annotations
+                }
+            , spec = Some spec
+            }
+
+in  mkIngress services
+
+```
+
+As before we get the yaml out by running:
+
+```bash
+dhall-to-yaml --omitEmpty < examples/ingress.dhall
+```
+
+Result:
+```yaml
+## examples/out/ingress.yaml
+
+apiVersion: networking.k8s.io/v1beta1
+kind: Ingress
+metadata:
+  annotations:
+    kubernetes.io/ingress.allow-http: "false"
+    kubernetes.io/ingress.class: nginx
+  name: nginx
+spec:
+  rules:
+    - host: foo.example.com
+      http:
+        paths:
+          - backend:
+              serviceName: foo
+              servicePort: 80
+    - host: default.example.com
+      http:
+        paths:
+          - backend:
+              serviceName: default
+              servicePort: 80
+  tls:
+    - hosts:
+        - foo.example.com
+      secretName: foo-certificate
+    - hosts:
+        - default.example.com
+      secretName: default-certificate
+
+```
+
+## FAQ
+
+#### Can I generate a YAML file with many objects in it?
+
+It is usual for k8s YAML files to include multiple objects separated by `---` ("documents" in YAML lingo),
+so you might want to do it too.
+
+If the objects have the same type, this is very easy: you return a Dhall list containing the
+objects, and use the `--documents` flag, e.g.:
+
+```bash
+dhall-to-yaml --documents --omitEmpty <<< "let a = ./examples/deploymentSimple.dhall in [a, a]"
+```
+
+If the objects are of different type, it's not possible to have separate documents in the same YAML file.  
+However, since [k8s has a builtin `List` type for these cases](https://github.com/kubernetes/kubernetes/blob/master/hack/testdata/list.yaml),
+it's possible to use it together with the [union type of all k8s types that we generate][typesUnion].
+
+So if we want to deploy e.g. a Deployment and a Service together, we can do:
+
+```dhall
+let k8s = ./typesUnion.dhall
+
+in 
+{ apiVersion = "v1"
+, kind = "List"
+, items = 
+  [ k8s.Deployment ./my-deployment.dhall
+  , k8s.Service ./my-service.dhall
+  ]
+}
+```
+
+
+## Projects Using `dhall-kubernetes`
+
+* [dhall-prometheus-operator][dhall-prometheus-operator]: Provides types and default records for [Prometheus Operators][prometheus-operator].
+
+
+## Development
+
+### Adding a new Kubernetes releases
+
+To add a new supported release, run:
+
+```bash
+./scripts/add-kubernetes-release.sh "${VERSION}"
+```
+
+If you want to make a specific release the preferred release, run:
+
+```
+$ echo "${VERSION}" > ./nix/preferred.txt
+$ ./scripts/generate.sh
+```
+
+### Tests
+
+All tests are defined in `release.nix`. We run these tests in CI in a [Hydra
+project][hydra-project].
+
+You can run the tests locally with the following command:
+
+```bash
+nix build --file ./release.nix
+```
+
+### Generating `types` `default` and `README.md`
+
+Running `scripts/generate.sh` will generate all dhall files from the kubernetes
+swagger specification, and copy them to `types` and `default`. It will also
+generate `README.md` from `docs/README.md.dhall`.
+
+If you make changes to `scripts/convert.py` or `docs/README.md.dhall`, you need
+to run this command afterwards.
+
+
+[stack]: https://haskellstack.org/
+[hydra-project]: http://hydra.dhall-lang.org/project/dhall-kubernetes
+[dhall-lang]: https://github.com/dhall-lang/dhall-lang
+[dhall-website]: https://dhall-lang.org/
+[security-hashes]: https://github.com/dhall-lang/dhall-lang/wiki/Safety-guarantees#code-injection
+[typesUnion]: https://github.com/dhall-lang/dhall-kubernetes/blob/master/typesUnion.dhall
+[kubernetes]: https://kubernetes.io/
+[normalization]: https://en.wikipedia.org/wiki/Normalization_property_(abstract_rewriting)
+[nginx-ingress]: https://github.com/kubernetes/ingress-nginx
+[dhall-tutorial]: http://hackage.haskell.org/package/dhall-1.28.0/docs/Dhall-Tutorial.html
+[deployment]: ./schemas/io.k8s.api.apps.v1.Deployment.dhall
+[Ingress]: ./schemas/io.k8s.api.extensions.v1beta1.Ingress.dhall
+[prometheus-operator]: https://github.com/coreos/prometheus-operator
+[dhall-prometheus-operator]: https://github.com/coralogix/dhall-prometheus-operator