fetch and update particular field using terraform - kubernetes

Question

i have a scenario,
How to fetch particular field value and also update particular field value?
For example :
Im deploying an application using terraform "kubernetes_deployment" resource configured with environment variables(endpoint=abc) and replicas=2.
resource "kubernetes_deployment" “app” {
…..….
spec {
replicas = 2
template {
spec {
….
env {
name = “ENDPOINT”
value = “abc”
}
}
Once i deployed using terraform script, another script might change configurations replicas=5 and environment values(endpoint=xyz)
Now i need to update only replicas to 20(if replicas < 20) through terraform script without changing the environment values(endpoint=abc)?
resource "kubernetes_deployment" “app” {
…..….
spec {
replicas = 20 -> only this has to reflect in apply
template {
spec {
….
env {
name = “ENDPOINT”
value = “abc”
}
}
How can i fetch particular field(replicas) to compare if replicas count > 20 and update only replicas count?
Can someone with more Terraform experience help me on this?

Answer 1

Inside the "kubernetes_deployment" resource block, consider adding a lifecycle block. Use it to ignore changes to resource attributes that can be made outside of Terraform's knowledge.
Provide a list of resource attributes to "ignore_changes", which Terrform would ignore in subsequent runs. The arguments are the relative address of the attributes in the resource. Map and list elements can be referenced using index notation.
lifecycle {
ignore_changes = [spec["env"]]
}
Reference: https://www.terraform.io/docs/language/meta-arguments/lifecycle.html#ignore_changes