Input Type | Jsonnet

Jsonnet is a superset of json format that includes features such as conditionals, variables and imports. Refer to jsonnet docs to understand how it works.

Note: unlike jinja2 templates, one jsonnet template can output multiple files (one per object declared in the file).

Accessing the inventory

Typical jsonnet files would start as follows:

local kap = import "lib/kapitan.libjsonnet"; #(1)!
local inv = kap.inventory(); #(2)!
local p = inv.parameters; #(3)!

{
    "data_java_opts": p.elasticsearch.roles.data.java_opts, #(4)!
}

1. Import the Kapitan inventory library.
2. Assign the content of the full inventory for this specific target to the inv variable.
3. Assign the content of the inventory.parameters to a variable p for convenience.
4. Use the p variable fo access a specific intentory value

Note: The dictionary keys of the jsonnet object are used as filenames for the generated output files. If your jsonnet is not a dictionary, but is a valid json(net) object, then the output filename will be the same as the input filename. E.g. 'my_string' is inside templates/input_file.jsonnet so the generated output file will be named input_file.json for example and will contain "my_string".

Jinja2 templating

Kapitan allows you to compile a Jinja template from within Jsonnet:

local kap = import "lib/kapitan.libjsonnet";

{
    "jon_snow": kap.jinja2_template("templates/got.j2", { is_dead: false }),
}

Callback functions

In addition, importing kapitan.libjsonnet makes available the following native_callback functions gluing reclass to jsonnet (amongst others):

inventoryjinja2_templateyamlfile I/Osha256_stringgzip_b64jsonschema

returns a dictionary with the inventory for target

renders the jinja2 file with context specified

yaml_loadyaml_load_streamyaml_dumpyaml_dump_stream

returns a json string of the specified yaml file

returns a list of json strings of the specified yaml file

returns a string yaml from a json string

returns a string yaml stream from a json string

file_readfile_existsdir_files_listdir_files_read

reads the file specified

returns informative object if a file exists

returns a list of file in a dir

returns an object with keys - file_name and values - file contents

returns sha256 of string

returns base64 encoded gzip of obj

validates obj with schema, returns object with 'valid' and 'reason' keys

Jsonschema validation

Given the follow example inventory:

mysql:
  storage: 10G
  storage_class: standard
  image: mysql:latest

The yaml inventory structure can be validated with the new jsonschema() function:

local schema = {
    type: "object",
    properties: {
        storage: { type: "string", pattern: "^[0-9]+[MGT]{1}$"},
        image: { type: "string" },
    }
};
// run jsonschema validation
local validation = kap.jsonschema(inv.parameters.mysql, schema);
// assert valid, otherwise error with validation.reason
assert validation.valid: validation.reason;

If validation.valid is not true, it will then fail compilation and display validation.reason.

Fails validation because storage has an invalid pattern (10Z)

Jsonnet error: failed to compile /code/components/mysql/main.jsonnet:
RUNTIME ERROR: '10Z' does not match '^[0-9]+[MGT]{1}$'

Failed validating 'pattern' in schema['properties']['storage']:
    {'pattern': '^[0-9]+[MGT]{1}$', 'type': 'string'}

On instance['storage']:
    '10Z'

/code/mysql/main.jsonnet:(19:1)-(43:2)

Compile error: failed to compile target: minikube-mysql