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Data Values

Overview ¶

A ytt run can be configured by supplying custom Data Values.

(For a high-level overview of ytt, see How it works.)

Declaring Data Values ¶

Typically, Data Values are declared in a schema file. See the Using Data Values guide for more details.

Note: ytt continues to support declaring Data Values without schema for backwards-compatibility. However, due to the significantly improved support for catching configuration errors that schema brings, it is the recommended method for doing so.

Configuring Data Values ¶

Data Values can be configured in one of two ways:

on the command-line via the family of command-line --data-value... flags,
in a “Data Values Overlay” document and included via the --file flag,

Configuring Data Values via command line flags ¶

The --data-value... family of command-line flags provides a means of configuring Data Values from:

the command-line, multiple values:
- --data-values-file — multiple values from a file, directory, URL, or standard in.
the command-line, directly, one at a time:
- --data-value — single value as a string.
- --data-value-yaml — single value decoded a YAML.
- --data-value-file — a single value to the contents of a file, URL, or standard in.
OS environment variables:
- --data-values-env — all OS variables with a named prefix, all as strings.
- --data-values-env-yaml — all OS variables with a named prefix, decoded as YAML.

Quick Example

export STR_VALS_key6=true
export YAML_VALS_key7=true

$ cat dev/values.yml
key1: values.yml-key1
key2:
  original: from values.yml

$ ytt \
  --data-value key1=val1-arg        \  # overrides key1 from dev/values.yml
  --data-value-yaml key2.nested=123 \  # merges into key2 from dev/values.yml
  --data-value-yaml 'key3.other={"nested": true}' \  # decoded to a map
  --data-value-file key4=client.crt \  # contains contents of client.crt
  --data-values-env STR_VALS        \  # decodes STR_VALS_key6 to a string
  --data-values-env-yaml YAML_VALS  \  # decodes YAML_VALS_key7 to a boolean
  --data-values-file dev/           \  # finds and uses dev/values.yml
  --data-values-inspect

yields:

key2:
  original: from values.yml
  nested: 123
key6: "true"
key7: true
key1: val1-arg
key3:
  other:
    nested: true
key4: <contents of client.crt>

Notes

the --data-value... flags can be repeated multiple times and used in any combination. The do not necessarily combine in the order supplied on the command-line; see Data Values merge order for details.
Where schema is used, --data-value... flags can only override values allowed by schema. Once schema is in use, all Data Values must be declared in schema files.
Where schema is not used, (as of v0.34.0) Data Values can be declared via --data-value... flags (previously, these flags could only override previously declared values). This is useful for ad-hoc templating situations (usually a shell script one-liner) involving one or two Data Values — where type checks and validations are less useful.

`--data-values-file` ¶

Sets one or more Data Values from a plain YAML file, a directory containing YAML files, an HTTP URL, or standard input.

--data-values-file [@lib:]path

path — one of: a filesystem path; an HTTP URL; or the dash character -.
- filesystem path can either be the path to a single YAML file or a directory that (recursively) contains one or more files that have either the .yaml or .yml extension. If a directory is specified, all non-YAML files are ignored.
- HTTP URL is expected to resolve to a stream of one or more YAML document(s).
- - is the UNIX convention for referring to standard input. When specified, stdin is expected to contain a plain YAML document.
  - The - file can only be used once in a ytt invocation.
  - this input is given the name stdin.yml.
@lib: — (optional) names the library whose data values to configure (details below) rather than the root library.

Not to be confused with --data-value-file which sets the value of exactly one Data Value.

Plain YAML Data Values

Regardless the source, the inputs for this flag must be plain YAML. It must not contain ytt templating (i.e. comments that start with #@.

When multiple YAML documents are given, they are merged:

each document is merged into the previous;
map values are merged (values for entries that were previously defined are merged within the same key, recursively; values for new keys are added to the map);
array values are replaced (last wins)

Examples:

Example 1: Single File

prod-values.yml

domain: example.com
client_opts:
  timeout: 10
  retry: 5

$ ytt ... --data-values-file prod-values.yml

sets all three Data Values:

domain=example.com (a string value)
client_opts.timeout=10 (an integer value)
client_opts.retry=5 (an integer value)

Example 2: Directory

See https://github.com/carvel-dev/ytt/tree/develop/examples/data-values-directory for a complete example and explanation.

Example 3: HTTP URL

Given https://raw.githubusercontent.com/carvel-dev/ytt/develop/examples/data-values/values-file.yml

$ ytt --data-values-file https://raw.githubusercontent.com/carvel-dev/ytt/develop/examples/data-values/values-file.yml --data-values-inspect

yields

nothing: something
string: str
bool: true
int: 124
new_thing: new

(Note the merged value of int:)

`--data-value` ¶

Sets a single Data Value to a string value.

--data-value [@lib:]key=value

key — name of Data Value. Use dot notation for nested values (e.g. key2.nested=val)
value — value to set (always interpreted as a string)
@lib: — (optional) specify library whose data values to configure (details below)
examples: instance.count=123, key=string, input=true, all set to strings

`--data-value-yaml` ¶

Sets a single Data Value to a YAML-parsed value.

--data-value-yaml [@lib:]key=value

key — name of Data Value.
value — value to set (decoded as a YAML value)
@lib: — (optional) specify library whose data values to configure (details below)
examples: instance.count=123 sets as integer, key=string as string, input=true as bool

`--data-value-file` ¶

Sets a single Data Value to the contents of: a given file, an HTTP URL, or standard input.

--data-value-file [@lib:]key=path

key — name of Data Value.
path — one of: a file path; an HTTP URL; or the dash character -.
- - is the UNIX convention for referring to standard input. The - file can only be used once in a ytt invocation.
@lib: — (optional) specify library whose data values to configure (details below)

This flag is particularly useful for loading multi-line string values from files such as private and public key files, certificates, etc.

Not to be confused with --data-values-file which sets the values of multiple Data Values.

`--data-values-env` ¶

Sets one or more Data Values to string values from OS environment variables that start with the given prefix.

--data-values-env [@lib:]PREFIX

PREFIX — the literal prefix used to select the set of environment variables from which to configure Data Values.
@lib: — (optional) specify library whose data values to configure (details below)

Setting Environment Variables

for nested values, use double-underscore (i.e. __) in environment variable names to denote a “dot”.

Examples

Example: With Nested Values

$ env
...
DVAL_key1=blue
DVAL_key2__nested=1337
...

$ ytt ... --data-values-env DVAL

would set two Data Values:

key1=blue (the string “blue”)
key2.nested="1337" (the string “1337”)

`--data-values-env-yaml` ¶

Sets one or more Data Values to the YAML-decoded values from OS environment variables that start with the given prefix.

--data-values-env-yaml [@lib:]PREFIX

PREFIX — the literal prefix used to select the set of environment variables from which to configure Data Values.
@lib: — (optional) specify library whose data values to configure (details below)
for nested values, use double-underscore (i.e. __) in environment variable names to denote a “dot”.

Examples

Example: With Nested Values

$ env
...
DVAL_key1=blue
DVAL_key2__nested=1337
...

$ ytt ... --data-values-env DVAL

would set two Data Values:

key1=blue (a string value)
key2.nested=1337 (an integer value)

Configuring Data Values via Data Values Overlays ¶

Data Values can also be configured via a specific kind of ytt Overlay.

A Data Values Overlay is a YAML document annotated with @data/values.

#@data/values
---
key1: val1
key2:
  nested: val2
key3: val3
key4:

Note:

data.values is a struct.

Splitting Data Values Overlays into multiple files ¶

Available in v0.13.0.

It’s possible to split data values into multiple files (or specify multiple data values in the same file). @ytt:data library provides access to the merged result. Merging is controlled via overlay annotations and follows same ordering as overlays. Example:

values-default.yml:

#@data/values
---
key1: val1
key2:
  nested: val2
key3:
key4:

values-production.yml:

#@data/values
---
key3: new-val3
#@overlay/remove
key4:
#@overlay/match missing_ok=True
key5: new-val5

Note that key4 is being removed, and key5 is marked as missing_ok=True because it doesn’t exist in values-default.yml (this is a safety feature to prevent accidental typos in keys).

config.yml:

#@ load("@ytt:data", "data")

first: #@ data.values.key1
third: #@ data.values.key3
fifth: #@ data.values.key5

Running ytt -f . (or ytt -f config.yml -f values-default.yml -f values-production.yml) results in:

first: val1
third: new-val3
fifth: new-val5

See Multiple data values example in the online playground.

Data Values merge order ¶

Data values are merged in following order (latter one wins):

default values from @data/values-schema files
@data/values overlays (same ordering as overlays)
--data-values-file (same ordering as overlays)
--data-values-env specified values (left to right)
--data-values-env-yaml specified values (left to right)
--data-value specified value (left to right)
--data-value-yaml specified value (left to right)
--data-value-file specified value (left to right)

(When configuring libraries, the data values merge order, is the same, even if through different mechanisms.)

Library data values ¶

Available in v0.28.0+

Each library may specify data values which will be evaluated separately from the root level library.

Setting library values via files ¶

To override library data values, add @library/ref annotation to data values YAML document, like so:

#@library/ref "@lib1"
#@data/values
---
key1: val1
key2: val2

#@library/ref "@lib1"
#@data/values after_library_module=True
---
key3: val3

The @data/values annotation also supports a keyword argument after_library_module. If this keyword argument is specified, given data values will take precedence over data values passed to the .with_data_values(...) function when evaluating via the library module.

Setting library values via command line flags ¶

Data value flags support attaching values to libraries for use during library module evaluation:

export STR_VALS_key6=true # will be string 'true'
export YAML_VALS_key6=true # will be boolean true

$ ytt -f . \
   --data-value @lib1:key1=val1-arg \
   --data-value-yaml @lib2:key2.nested=123 \ # will be int 123
   --data-value-yaml '@lib3:key3.other={"nested": true}' \
   --data-value-file @lib4:key4=/path \
   --data-values-env @lib5:STR_VALS \
   --data-values-env-yaml @lib6:YAML_VALS
   --data-values-file @lib6:/path

export STR_VALS_key6=true
export YAML_VALS_key7=true

$ cat dev/values.yml
key1: values.yml-key1
key2:
  original: from values.yml

$ ytt \
  --data-value @lib1:key1=val1-arg        \  # overrides key1 from dev/values.yml
  --data-value-yaml @lib1:key2.nested=123 \  # merges into key2 from dev/values.yml
  --data-value-yaml '@lib2:key3.other={"nested": true}' \  # decoded to a map
  --data-value-file @lib2:key4=client.crt \  # contains contents of client.crt
  --data-values-env @lib2:STR_VALS        \  # decodes STR_VALS_key6 to a string
  --data-values-env-yaml @lib1:YAML_VALS  \  # decodes YAML_VALS_key7 to a boolean
  --data-values-file @lib1:dev/              # finds and uses dev/values.yml

sends the following Data Values to library lib1:

key2:
  original: from values.yml
  nested: 123
key7: true
key1: val1-arg

and the following Data Values to library lib2:

key6: "true"
key3:
  other:
    nested: true
key4: <contents of client.crt>

Library Data Values merge order ¶

For a given library instance, data values are merged in following order (latter one wins):

default values from schema:
1. @data/values-schema files within the library
2. @data/values-schema files externally referenced in.
3. given through instance.with_data_values_schema()
4. @data/values-schema files externally referenced in after_library_module=True.
values from data value sources:
1. @data/values overlays within the library (same ordering as overlays)
2. @data/values overlays externally referenced in
3. specified using instance.with_data_values()
4. @data/values overlays externally referenced in after_library_module=True
5. --data-values-file specified files referenced in (same ordering as overlays)
6. --data-values-env specified values referenced in (left to right)
7. --data-values-env-yaml specified values referenced in (left to right)
8. --data-value specified value referenced in (left to right)
9. --data-value-yaml specified value referenced in (left to right)

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