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ytt @data/values

Defining data values

One way to inject input data into templates is to include a YAML document annotated with @data/values. Example:

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

Subsequently these values can be accessed via @ytt:data library:

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

first: #@ data.values.key1
second: #@ data.values.key2.nested
third: #@ data.values.key3
fourth: #@ data.values.key4

Resulting in

first: val
second: val2
third: null
fourth: null

Splitting data values 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

config.yml:

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

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

Results in

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

See Multiple data values example in the online playground.

Overriding data values via command line flags

(As of v0.17.0+ --data-value parses value as string by default. Use --data-value-yaml to get previous behaviour.)

ytt CLI allows to override input data via several CLI flags:

  • --data-value (format: key=val) can be used to set a specific key to string value
    • dotted keys (e.g. key2.nested=val) are interpreted as nested maps
    • examples: key=123, key=string, key=true, all set to strings
  • --data-value-yaml (format: key=yaml-encoded-value) same as --data-value but parses value as YAML
    • examples: key=123 sets as integer, key=string as string, key=true as bool
  • --data-value-file (format: key=/file-path) can be used to set a specific key to a string value of given file contents
    • dotted keys (e.g. key2.nested=val) are interpreted as nested maps
    • this flag can be very useful when loading multine line string values from files such as private and public key files, certificates
  • --data-values-env (format: DVAL) can be used to pull out multiple keys from environment variables based on a prefix
    • given two environment variables DVAL_key1=val1-env and DVAL_key2__nested=val2-env, ytt will pull out key1=val1-env and key2.nested=val2-env variables
    • interprets values as strings
  • --data-values-env-yaml (format: DVAL) same as --data-values-env but parses values as YAML

These flags can be repeated multiple times and used together. Flag values are merged into data values last.

Note that for override to work data values must be defined in at least one @data/values YAML document.

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

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