Allow more flexible chart options

[lukehoban]

Fixes #255.
Fixes #229.
Fixes #257.

Align more closely with helm options for chart references to support all scenarios supported by Helm including (a) getting latest by passing no version (b) using explicitly repo URLs (c) providing fully qualified URLs to charts.

All of the following now work:

// 1. Explicit repo/chart/version - not technically part of `helm` format but needed for back compat
repo: "stable",
chart: "nginx-lego",
version: "0.3.1",

// 2. Reference to "latest"
repo: "stable",
chart: "nginx-lego",

// 3. Helm "chart reference"
chart: "stable/nginx-lego",

// 4. Helm "chart reference" with explicit version
chart: "stable/nginx-lego",
version: "0.3.1"

// 5. Helm "chart reference and repo url" with explicit version
chart: "nginx-lego",
version: "0.3.1",
fetchOpts: {
  repo: "https://kubernetes-charts.storage.googleapis.com"
},

// 6. Helm "chart reference and repo url" 
chart: "nginx-lego",
fetchOpts: {
  repo: "https://kubernetes-charts.storage.googleapis.com"
},

// 7. Helm "absolute URL" 
chart: "https://kubernetes-charts.storage.googleapis.com/nginx-lego-0.3.1.tgz",

[hausdorff]

This is the sort of patch where you think: why didn't I do it this way to begin with?

[hausdorff]

Actually, I just tried this:

export const istio = new k8s.helm.v2.Chart(
    appName,
    {
        repo: "https://istio.io/charts",
        chart: "istio",
        namespace: namespace.metadata.apply(m => m.name),
        version: "1.0.1",
        // fetchOpts: { repo:  },
        // for all options check https://github.com/istio/istio/tree/master/install/kubernetes/helm/istio
        values: { kiali: { enabled: true } }
    },
    { dependsOn: [namespace], providers: { kubernetes: k8sProvider } }
);

and also this:

export const istio = new k8s.helm.v2.Chart(
    appName,
    {
        chart: "istio",
        namespace: namespace.metadata.apply(m => m.name),
        version: "1.0.1",
        fetchOpts: { repo: "https://istio.io/charts" },
        // for all options check https://github.com/istio/istio/tree/master/install/kubernetes/helm/istio
        values: { kiali: { enabled: true } }
    },
    { dependsOn: [namespace], providers: { kubernetes: k8sProvider } }
);

both of these result in this:

    error: Error: Command failed: helm fetch https\://istio.io/charts/istio --untar --version 1.0.1 --destination /var/folders/w5/n_5_kc696xxb8h9rd8d3px2r0000gp/T/tmp-41891FR25WX35Q094
    Error: Failed to fetch https://istio.io/charts/istio : 404 Not Found

Am I misunderstanding the API?

[lukehoban]

Is that really where that chart lives? I get the same from helm:

$ helm fetch --repo https://istio.io/charts istio
Error: Failed to fetch https://istio.io/istio-1.0.1.tgz : 404 Not Found

[lukehoban]

Looks like there is a bug in helm here where a missing trailing slash makes helm fetch --repo <url> not work, but the same missing slash is okay in helm repo add <url>. I guess we can work around that bug and make sure there is always a trailing slash?

[lukehoban]

Opened helm/helm#4954 to track the issue in helm.

I'm not sure it makes sense to workaround this in our layer - the fetchOpts are semantically exactly flags to helm, so trying to "fix" them up feels wrong.

Were we to have done something here where we allowed this - I could imagine us adding the workaround to it - but we haven't added support for this form at all (because it isn't really something helm supports):

repo: "https://istio.io/charts",
chart: "istio",

Given that, I'll go ahead and merge this in as is for now.