Terraform Jsonencode Function – Definition & Examples

The jsonencode function in Terraform converts a Terraform value (such as a map, list, or object) into a JSON-formatted string. It’s typically used when a resource or module expects a JSON string input, such as an IAM policy in AWS or a role definition in Azure. 

The jsondecode function in Terraform converts a JSON-formatted string into a native Terraform value (map, list, string, number, etc.). It is the opposite of the jsonencode function and is typically used to parse external data passed as a JSON string, such as data from a file, remote source, or environment variable. 

Read more about other Terraform functions, expressions, and loops.

To play around with the jsonencode function, you can use the Terraform console. Simply type terraform console into your terminal to start.

Enter jsonencode({"hello"="world"}) — The output displayed will be in JSON format.

Note that the jsonencode cannot directly map to all types available in JSON formatting because there are differences between how the types are represented between HCL (Hashicorp configuration language) and JSON.

Terraform to JSON data types are mapped as follows:

JSON lacks constructs for distinguishing set from list, or object from map, so type constraints and uniqueness/order guarantees are lost.

For the following examples, we will create a simple JSON file:

yoda.json

Example 1: Using JSON files as input variables and local variables

In this example, we will use the yoda.json file as an input variable, have Terraform use the jsondecode function in the locals, and then finally output the results.

1. We define a variable json_input to specify the path to the JSON input file.
2. We decode the JSON content using the jsondecode function and store it in the local.input_data variable. The file function specifies we need to read the JSON contents from a file.
3. We define outputs for each key in the JSON, making the data available for other parts of your Terraform code. You can reference it elsewhere in your Terraform code using local.input_data.name, local.input_data.age, and local.input_data.city.

To run the code, in your terminal, specify the variable directly with the -var flag, which points to the path of the yoda.json file:

Example 2: Passing in JSON via environment variables

In this example, we will define some JSON as an environment variable and pass it into our Terraform configuration.

To set the environment variables, run the following on the terminal:

Environment variables can be used to set Terraform variables using TF_VAR.

The _json_imput part defines the name of the variable we want to set. This can then be referenced directly in the Terraform code (without the need for the file function this time):

To see the results, run:

Example 3: Decoding JSON strings to Terraform maps

In this example, we will output the values as a Terraform map and pass the JSON in directly on the terminal.

Note that the outputs now have the values for each key contained in [""] .

To test the output we can run:

Example 4: Using jsonencode in the template file

Suppose you have a template file, for example, a configuration file, and you want to include some data as a JSON-encoded string in that file.

Our template file looks like this:

Our Terraform configuration looks like this:

example4.tf

First, you define the data you want to encode as a JSON string. This data could be a variable or a map within your Terraform configuration.

Next, we use the data "template_file" block to render a template file. The template attribute specifies the path to the template file, which is template.tpl. The vars attribute is used to pass variables into the template. In this case, we’re passing the app_config variable, but we use the jsonencode function to encode it as a JSON string.

Finally, we create a local file using the resource "local_file" block. This local file is used to save the generated JSON configuration.

We specify the filename attribute to set the path and name of the output file, which is app_config.json. The content attribute contains the rendered output from the template defined in the data "template_file" block. This content is obtained using data.template_file.app_config_template.rendered.

To run the example:

On confirming the apply, a file called app_config.json will be generated in the local directory containing the map contents in JSON format:

Example 5: Using jsonencode with the for loop

You can use jsonencode in conjunction with a for loop in Terraform to generate JSON data structures dynamically. In this example, we have a list of items, which we will encode into a JSON array using a for loop.

Our template.tpl file looks like this:

example5.tf:

This time, inside the vars block, we use a for loop to iterate over each item in the var.items list. In each iteration, we create a map with the key “name” and the value as the current item. This list of maps is then passed to jsonencode to create a JSON array.

On confirmation of the apply, an items.json file is generated in the local directory containing the following JSON:

Example 6: Creating IAM policies using jsonencode function

Creating IAM policies in Terraform using the jsonencode function can be useful when you need to define fine-grained permissions for your AWS resources.

IAM policies are defined as JSON documents, and you can use the jsonencode function to create these policy documents in your Terraform configuration.

1. The variable iam_policy_statements represents a list of IAM policy statements. Each statement includes an action (a list of allowed actions) and a resource (the AWS resource to which the actions apply).
2. The jsonencode function in the locals block generates the JSON document for the IAM policy. We use a for loop to iterate over the policy statements defined in the variable and structure them into the required format.
3. The IAM policy is created using the aws_iam_policy resource. This resource’s policy attribute is set to the JSON-encoded IAM policy document from the locals block.
4. Finally, you can attach the created policy to an IAM user, group, or role as needed by referencing the aws_iam_policy.example resource in the respective resource block (aws_iam_user_policy_attachment, aws_iam_group_policy_attachment, or aws_iam_role_policy_attachment).

Example 7: Creating Azure Policy definitions with jsonencode function

Azure Policy definitions are typically defined as JSON objects, and you can use jsonencode to create those JSON objects within your Terraform configuration.

The below example shows an Azure policy rule enforcing restrictions if certain tags are applied. You can reference it elsewhere in your code by referring to policy_rule.

After defining the policy, you can associate it with a policy assignment to enforce it within a particular scope, such as the subscription level:

jsonencode converts a Terraform expression (like a map or list) into a valid JSON string. It’s commonly used when passing structured data to APIs or templates that expect JSON. jsondecode does the reverse. It parses a JSON string and turns it into a Terraform expression you can use in logic or interpolation.

jsonencode is specifically for encoding structured data into a JSON string, making it suitable for creating JSON-based configuration files or policy definitions. Heredoc is a way to include multi-line strings directly in your Terraform configuration.

Heredoc allows you to define a block of text without escaping special characters or worrying about JSON formatting. It is often used to embed text, scripts, or configuration files in your Terraform code.

For reference, Heredoc syntax within a resource block looks like the following:

Use jsonencode when precision and structural correctness matter, such as rendering data for APIs or configuration files and heredoc for readable templates or inline file content.

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Using the JSON encode and the opposite jsondecode functions, you can handle JSON files in your Terraform configuration files. Data structures can be manipulated as needed to read in or create new JSON files for common purposes, such as IAM assignments in AWS or creating Azure Policy.

Frequently asked questions

What does jsonencode() do in Terraform?

jsonencode() converts any valid Terraform value (string, number, list, map, object, etc.) into a compact JSON string. It minifies the output by design, removing all unnecessary whitespace. 

How to escape quotes or special characters?

Escaping is handled automatically. For example, double quotes (") inside strings become \", and newline characters become \n. You don’t need to manually escape special characters unless you’re nesting the resulting JSON inside another string (e.g., a template or shell command), in which case you might need additional escaping layers.

Does jsonencode pretty-print?

No, jsonencode() always emits one-line, minified JSON. This behavior is by design and cannot currently be changed.

To pretty-print the JSON for readability, you can:

• Pipe the value through the Terraform console:
  terraform console <<< 'jsonencode(var.example)' | jq
• Use templatefile() with manual indentation logic (though it’s tedious and error-prone).
  

Is the encoded JSON stored in the state file?

Yes. If you use jsonencode() inside a local, output, or resource block, its result can be persisted in the Terraform state file.

As a best practice:

• Mark outputs containing sensitive data with sensitive = true
• Use secure state backends (e.g., S3 with encryption, Terraform Cloud, etc.)
• Avoid placing secrets in values encoded via jsonencode(), if possible

Does jsonencode support YAML?

No. jsonencode() is strictly for JSON. For YAML support, use yamlencode() to convert a Terraform value to YAML and yamldecode() to parse YAML into a Terraform value.

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