{"id":7586,"date":"2023-08-01T19:29:23","date_gmt":"2023-08-01T19:29:23","guid":{"rendered":"https:\/\/www.devopsschool.com\/blog\/?p=7586"},"modified":"2023-08-01T19:29:25","modified_gmt":"2023-08-01T19:29:25","slug":"how-to-use-one-modules-variable-in-another-module-in-terraform","status":"publish","type":"post","link":"https:\/\/www.devopsschool.com\/blog\/how-to-use-one-modules-variable-in-another-module-in-terraform\/","title":{"rendered":"How to use one module’s variable in another module in terraform?"},"content":{"rendered":"\n
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To get the output from one module to another module in Terraform, you can use the following steps:<\/p>\n\n\n\n

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  1. Define the output in the first module.<\/li>\n\n\n\n
  2. Import the second module.<\/li>\n\n\n\n
  3. Reference the output of the first module in the second module.<\/li>\n<\/ol>\n\n\n\n

    Here is an example of how to do this:<\/p>\n\n\n\n

    <\/p>\n\n\n

    # First module<\/span>\r\nmodule \"web_server\"<\/span> {\r\n  source = \".\/web_server\"<\/span>\r\n\r\n  output \"instance_ip_addr\"<\/span> {\r\n    value = aws_instance.web_server.public_ip\r\n  }\r\n}\r\n\r\n# Second module<\/span>\r\nmodule \"database\"<\/span> {\r\n  source = \".\/database\"<\/span>\r\n\r\n  instance_ip_addr = module.web_server.instance_ip_addr\r\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
    In this example, the web_server<\/code> module defines an output called instance_ip_addr<\/code>. The database<\/code> module imports the web_server<\/code> module and then references the instance_ip_addr<\/code> output in its own configuration.<\/p>\n\n\n\n
    When you run terraform apply<\/code>, Terraform will create the resources defined in both modules. The database<\/code> module will use the instance_ip_addr<\/code> output from the web_server<\/code> module to connect to the web server.<\/p>\n\n\n\n
    Here is an explanation of the code:<\/p>\n\n\n\n
      \n
    • The source<\/code> attribute in the module<\/code> block specifies the location of the module definition. In this case, the module definition is located in the web_server<\/code> directory.<\/li>\n\n\n\n
    • The output<\/code> block defines an output called instance_ip_addr<\/code>. The value of the output is the public IP address of the web server instance.<\/li>\n\n\n\n
    • The source<\/code> attribute in the module<\/code> block specifies the location of the module definition. In this case, the module definition is located in the database<\/code> directory.<\/li>\n\n\n\n
    • The instance_ip_addr<\/code> attribute references the instance_ip_addr<\/code> output from the web_server<\/code> module.<\/li>\n<\/ul>\n\n\n\n
      \n\n\n\n
      You can use outputs to accomplish this. In Terraform, a module can also return values. Again, this is done using a mechanism you already know: output variables.  Such as if there are 2 modules, kafka and cloudwatch.<\/p>\n\n\n\n
      In your kafka module, you could define an output that looks something like this:<\/p>\n\n\n
      \noutput \"instance_ids\"<\/span> {\n  value = [\"${aws_instance.kafka.*.id}\"<\/span>]\n}<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
      Case 1 – If you are calling kafka module from cloudwatch module by instantiated the module with something like:<\/strong><\/p>\n\n\n
      \nmodule \"kafka\"<\/span> {\n  source = \".\/modules\/kafka\"<\/span>\n}\n\n# You can then access that output as follows:<\/span>\ninstances = [\"${module.kafka.instance_ids}\"<\/span>]<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
      Case 2 – If your modules are isolated from each other (i.e. your cloudwatch module doesn’t instantiate your kafka module), you can pass the outputs as variables between modules:<\/strong><\/p>\n\n\n
      \nmodule \"kafka\"<\/span> {\n  source = \".\/modules\/kafka\"<\/span>\n}\n\nmodule \"cloudwatch\"<\/span> {\n  source = \".\/modules\/cloudwatch\"<\/span>\n  instances = [\"${module.kafka.instance_ids}\"<\/span>]\n}\n\n# Of course, your \"cloudwatch\" module would have to declare the instances variable.<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
      Case 3 – You can add the ASG name as an output variable in \/modules\/services\/webserver-cluster\/outputs.tf as follows.<\/strong><\/p>\n\n\n
      output \"asg_name\"<\/span> {\n  value       = aws_autoscaling_group.example.name\n  description = \"The name of the Auto Scaling Group\"<\/span>\n}\n\nYou can access module<\/span> output variables the same way as<\/span> resource output attributes. The syntax is:\n\nmodule<\/span>.<MODULE_NAME>.<OUTPUT_NAME>\nmodule<\/span>.frontend.asg_name<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n