如何在Terraform中将list类型参数cat设置为可选参数

原始配置 #

abc:
  - vm_name: "abc"
    template:
      cate: Apple
      image: "ubuntu18"
    cpu_cores: 1
    memory: 1024
    cat:
      - red
      - geen
      - blue
  - vm_name: "xyz"
    template:
      cate: Orange
      image: "ubuntu18"
    cpu_cores: 1
    memory: 1024
    cat:
      - red
      - blue
      - yellow
      - black

原始分组代码 #

用以下Terraform代码可将VM按cat字段的颜色分组：

locals {
  cfg_vars = yamldecode(file("test1.yaml"))
  list_color = flatten(local.config_vars["abc"][*]["cat"])

  inventory_map = merge([for color in local.list_color: {
    for vm in local.cfg_vars["abc"]:
      color => vm.vm_name... if contains(vm.cat, color)
      } 
  ]...)
}

原始运行结果 #

执行后local.inventory_map的分组结果如下：

{     
  "black" = [
    "xyz",  
  ]         
  "blue" = [
    "abc",  
    "xyz",  
  ]         
  "geen" = [  
    "abc",    
  ]        
  "red" = [   
    "abc",               
    "xyz",               
  ]           
  "yellow" = [           
    "xyz",               
  ]                       
}        

问题场景 #

现在需要让cat参数成为可选字段，当配置中存在未定义cat的VM（如下方的efg）时，原始代码会因找不到cat字段报错，需修改代码兼容该场景，同时保持分组结果和之前一致。

带可选cat参数的配置示例：

abc:
  - vm_name: "abc"
    template:
      cate: Apple
      image: "ubuntu18"
    cpu_cores: 1
    memory: 1024
    cat:
      - red
      - geen
      - blue
  - vm_name: "xyz"
    template:
      cate: Orange
      image: "ubuntu18"
    cpu_cores: 1
    memory: 1024
    cat:
      - red
      - blue
      - yellow
      - black
  - vm_name: "efg"
    template:
      cate: Orange
      image: "ubuntu18"
    cpu_cores: 1
    memory: 1024

修改后的兼容代码 #

通过lookup函数处理可选字段，当cat不存在时返回空列表，既避免报错又自动过滤无颜色的VM：

locals {
  cfg_vars = yamldecode(file("test1.yaml"))
  # 遍历所有VM，用lookup获取cat，不存在则返回空列表，再扁平化得到所有颜色
  list_color = flatten([for vm in local.cfg_vars["abc"] : lookup(vm, "cat", [])])

  inventory_map = merge([for color in local.list_color: {
    for vm in local.cfg_vars["abc"]:
      # 同样用lookup处理每个VM的cat字段，空列表时contains返回false，自动跳过该VM
      color => vm.vm_name... if contains(lookup(vm, "cat", []), color)
      } 
  ]...)
}

预期运行结果 #

修改后执行代码，local.inventory_map会和原始结果一致：

{     
  "black" = [
    "xyz",  
  ]         
  "blue" = [
    "abc",  
    "xyz",  
  ]         
  "geen" = [  
    "abc",    
  ]        
  "red" = [   
    "abc",               
    "xyz",               
  ]           
  "yellow" = [           
    "xyz",               
  ]                       
} 

内容的提问来源于stack exchange，提问作者drmaa