Parameterizing

Deploying using Tanka worked well, but it did not really improve the situation in terms of maintainability and readability.

To do so, the following sections will explore some ways Jsonnet provides us with.

Functions parameters

Defining our deployment in a single block is not the best solution. Luckily with Jsonnet we can split our configuration into smaller, self-contained chunks.

Let’s start by creating a new function in main.jsonnet responsible for creating a Grafana deployment:

environments/default/main.jsonnet

local grafana() = {
  deployment: {
    apiVersion: 'apps/v1',
    kind: 'Deployment',
    metadata: {
      name: 'grafana',
    },
    spec: {
      selector: {
        matchLabels: {
          name: 'grafana',
        },
      },
      template: {
        metadata: {
          labels: {
            name: 'grafana',
          },
        },
        spec: {
          containers: [
            {
              image: 'grafana/grafana',
              name: 'grafana',
              ports: [{
                  containerPort: 3000,
                  name: 'ui',
              }],
            },
          ],
        },
      },
    },
  },
  service: {
    apiVersion: 'v1',
    kind: 'Service',
    metadata: {
      labels: {
        name: 'grafana',
      },
      name: 'grafana',
    },
    spec: {
      ports: [{
          name: 'grafana-ui',
          port: 3000,
          targetPort: 3000,
      }],
      selector: {
        name: 'grafana',
      },
      type: 'NodePort',
    },
  },
};

and let’s use it in our main configuration:

environments/default/main.jsonnet

local grafana() = {
  #  ...
};

{
  grafana: {
    # ...
  },
  grafana: grafana(),
  prometheus: #...
};

We can then replace hardcoded values by adding parameters to our function:

environments/default/main.jsonnet

local grafana() = {
local grafana(name, port) = {
  deployment: {
    apiVersion: 'apps/v1',
    kind: 'Deployment',
    metadata: {
      name: 'grafana',
      name: name,
    },
    spec: {
      selector: {
        matchLabels: {
          name: 'grafana',
          name: name,
        },
      },
      template: {
        metadata: {
          labels: {
            name: 'grafana',
            name: name,
          },
        },
        spec: {
          containers: [
            {
              image: 'grafana/grafana',
              name: 'grafana',
              name: name,
              ports: [{
                  containerPort: 3000,
                  containerPort: port,
                  name: 'ui',
              }],
            },
          ],
        },
      },
    },
  },
  service: {
    apiVersion: 'v1',
    kind: 'Service',
    metadata: {
      labels: {
        name: 'grafana',
        name: name,
      },
      name: 'grafana',
      name: name,
    },
    spec: {
      ports: [{
        name: 'grafana-ui',
        port: 3000,
        targetPort: 3000,
        name: '%s-ui' % name, // printf-style formatting
        port: port,
        targetPort: port,
      }],
      selector: {
        name: 'grafana',
        name: name,
      },
      type: 'NodePort',
    },
  },
};

and update the usage accordingly:

environments/default/main.jsonnet

local grafana(name, port) = {
  # ...
};

{
  grafana: grafana(),
  grafana: grafana('grafana', 3000),
  prometheus: #...
};

Tip

You can also set default values for function parameters:

local grafana(name='grafana', port=3000) = {
  # ...
};

Now we do not only have a single place to change tunables, but also won’t suffer from mismatching labels and selectors anymore, as they are defined in a single place and all changed at once.

Task

Now do the same for the Prometheus deployment by creating a function prometheus that takes a name and a port as parameters.