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# Merge (2-way)
2-way merges fields from a source to a destination, overriding the destination fields
where they differ.
### Merge Rules
Fields are recursively merged using the following rules:
- scalars
- if present only in the dest, it keeps its value
- if present in the src and is non-null, take the src value -- if `null`, clear it
- example src: `5`, dest: `3` => result: `5`
- non-associative lists -- lists without a merge key
- if present only in the dest, it keeps its value
- if present in the src and is non-null, take the src value -- if `null`, clear it
- example src: `[1, 2, 3]`, dest: `[a, b, c]` => result: `[1, 2, 3]`
- map keys and fields -- paired by the map-key / field-name
- if present only in the dest, it keeps its value
- if present only in the src, it is added to the dest
- if the field is present in both the src and dest, and the src value is
`null`, the field is removed from the dest
- if the field is present in both the src and dest, the value is recursively merged
- example src: `{'key1': 'value1', 'key2': 'value2'}`,
dest: `{'key2': 'value0', 'key3': 'value3'}`
=> result: `{'key1': 'value1', 'key2': 'value2', 'key3': 'value3'}`
- associative list elements -- paired by the associative key
- if present only in the dest, it keeps its value in the list
- if present only in the src, it is added to the dest list
- if the field is present in both the src and dest, the value is recursively merged
### Associative Keys
Associative keys are used to identify "same" elements within 2 different lists, and merge them.
The following fields are recognized as associative keys:
[`mountPath`, `devicePath`, `ip`, `type`, `topologyKey`, `name`, `containerPort`]
Any lists where all of the elements contain associative keys will be merged as associative lists.
### Example
> Source
apiVersion: apps/v1
kind: Deployment
spec:
replicas: 3 # scalar
template:
spec:
containers: # associative list -- (name)
- name: nginx
image: nginx:1.7
command: ['new_run.sh', 'arg1'] # non-associative list
- name: sidecar2
image: sidecar2:v1
> Destination
apiVersion: apps/v1
kind: Deployment
spec:
replicas: 1
template:
spec:
containers:
- name: nginx
image: nginx:1.6
command: ['old_run.sh', 'arg0']
- name: sidecar1
image: sidecar1:v1
> Result
apiVersion: apps/v1
kind: Deployment
spec:
replicas: 3 # scalar
template:
spec:
containers: # associative list -- (name)
- name: nginx
image: nginx:1.7
command: ['new_run.sh', 'arg1'] # non-associative list
- name: sidecar1
image: sidecar1:v1
- name: sidecar2
image: sidecar2:v1
|
