Terraform manages infrastructure using a <code>state</code> file, which is stored by default as <code>terraform.tfstate</code>. This works fine when working alone, but if multiple people manage the infrastructure simultaneously, conflicts may arise.
<figure class="image"><img src="https://api.reliasoftware.com/uploads/terraform_conflicts_56c78b355b.webp" alt="Terraform's Problem" width="788" height="569">
<figcaption>Terraform's Problem (Source: <a href="https://www.firefly.ai/academy/understanding-state-locking-and-versioning-in-terraform" rel="nofollow noreferrer">Firefly</a>)</figcaption>
</figure>
To solve this issue, Terraform provides the <code>backend</code> block to configure where the <code>state</code> file is stored.
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<ul>
<li>How To <a href="https://reliasoftware.com/blog/provisioning-a-docker-container-with-terraform">Use Terraform for Provisioning A Docker Container</a>?</li>
<li>How to <a href="https://reliasoftware.com/blog/ec2-to-ecs-migration">Migrate Your AWS Workloads from EC2 to ECS</a>?</li>
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<h2 data-start="0" data-end="32">What is Terraform Backend?</h2>
A Terraform backend defines how and where Terraform stores its state file (<code data-start="139" data-end="158">terraform.tfstate</code>). This state file keeps track of the resources Terraform manages such as AWS instances, Azure services, or any infrastructure created using Terraform. Without it, Terraform won&rsquo;t know what exists or what needs to be changed.
By default, the state is stored locally on your machine, but that becomes problematic when:
<ul>
<li data-start="488" data-end="549">Multiple team members are working on the same infrastructure.</li>
<li data-start="552" data-end="639">You want centralized control, locking, or history/versioning of infrastructure changes.</li>
<li data-start="642" data-end="700">You need the state file to persist beyond a single device.</li>
</ul>
To solve these issues, Terraform supports using remote backends like&nbsp;Amazon S3,&nbsp;Terraform Cloud,&nbsp;Azure Blob Storage,&nbsp;Google Cloud Storage, and more.&nbsp;With a Terraform remote backend, you are allowed:
<ul>
<li data-start="905" data-end="945">Shared access to the same state file</li>
<li data-start="948" data-end="997">State locking to prevent simultaneous updates</li>
<li data-start="1000" data-end="1031">Versioning and audit trails</li>
<li data-start="1034" data-end="1069">Better security and scalability</li>
</ul>
<h2>Terraform Backend Config</h2>
The <code>backend</code> block is placed at the beginning inside the <code>terraform</code> block. For example: Remote backend with Terraform Cloud:
<pre class="language-yaml"><code>terraform {
 backend "remote" {
 organization = "learning-journey"

 workspaces {
 name = "demo01"
 }
 }
}</code></pre>
Terraform provides multiple <code>backend</code> options, meaning different locations to store the <code>state</code> file, such as <code>local</code>, <code>remote</code>, <code>s3</code>, <code>azurerm</code>, etc. The default storage location is <code>local</code>.
<h2>Backend Types</h2>
As mentioned earlier, Terraform supports multiple backend types, but in this article, we will focus on <code>local</code> and <code>s3</code>.
<h3>Local</h3>
The local backend stores the <code>state</code> file on the user's machine.
Configuration:
<pre class="language-yaml"><code>terraform {
 backend "local" {
 path = "relative/path/to/terraform.tfstate"
 }
}</code></pre>
<code>path</code>: Specifies where the state file is stored. By default, it is <code>terraform.tfstate</code> in the root module.
While easy to set up, the local backend is not recommended for teams. It doesn&rsquo;t support locking, remote access, or version control, so conflicts may arise when multiple users manage infrastructure. Therefore, storing the state file in a shared location helps solve these conflicts, which is where the s3 backend comes in.
<h3>S3</h3>
With this Terraform S3 backend, the&nbsp;<code>state</code> file is stored in an S3 bucket. To ensure consistency, there are two ways to lock the state file:
<ul>
<li>S3 state locking (<code>use_lockfile</code>), available in <code>Terraform 1.10 and later</code>.</li>
<li>DynamoDB (<code>dynamodb_table</code>), where the partition key is <code>LockID</code> with a data type of <code>string</code>.</li>
</ul>
Example: Create an S3 bucket and a DynamoDB table on AWS.
<ul>
<li>Configuration:</li>
</ul>
<pre class="language-yaml"><code>terraform {
 backend "s3" {
 bucket = "mybucket"
 key = "your-state.tfstate"
 region = "us-east-1"
 profile = "Your_Profile"
 dynamodb_table = "states_tb"
 }
}</code></pre>
<ul>
<li>If using an AWS profile with S3 access permissions, no additional S3 permissions are required. Otherwise, you must configure permissions for reading and writing objects in S3:</li>
</ul>
<pre class="language-yaml"><code>{
 "Version": "2012-10-17",
 "Statement": [
 {
 "Effect": "Allow",
 "Action": "s3:ListBucket",
 "Resource": "arn:aws:s3:::mybucket"
 },
 {
 "Effect": "Allow",
 "Action": ["s3:GetObject", "s3:PutObject"],
 "Resource": [
 "arn:aws:s3:::mybucket/path/to/my/key",
 "arn:aws:s3:::mybucket/path/to/my/key.tflock"
 ]
 }
 ]
}</code></pre>
<ul>
<li>If using DynamoDB for state locking, you must also set permissions for DynamoDB on AWS (if the profile lacks necessary permissions):</li>
</ul>
<pre class="language-yaml"><code>{
 "Version": "2012-10-17",
 "Statement": [
 {
 "Effect": "Allow",
 "Action": [
 "dynamodb:DescribeTable",
 "dynamodb:GetItem",
 "dynamodb:PutItem",
 "dynamodb:DeleteItem"
 ],
 "Resource": "arn:aws:dynamodb:*:*:table/mytable"
 }
 ]
}</code></pre>
<h2>Practices</h2>
This section demonstrates how to configure and verify Terraform remote state storage using Amazon S3, and how to enable state locking using either S3-native lockfile or DynamoDB.
<h3>Storing State in S3</h3>
<ul>
<li>Modify <code>main.tf</code> to include the <code>backend</code> block inside the <code>terraform</code> block:</li>
</ul>
<pre class="language-yaml"><code>terraform {
 backend "s3" {
 bucket = "terraform-learning-demo01"
 key = "terraform.tfstate"
 region = "us-east-1"
 profile = "saa"
 }

 ...
}</code></pre>
<ul>
<li>Firstly, create an S3 bucket on AWS with a name matching the bucket field in the backend block. Here, we use <code>terraform-learning-demo01</code>. If not, we will encounter this issue:</li>
</ul>
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://api.reliasoftware.com/uploads/issue_with_creating_an_s3_bucket_ccfbb03687.webp" alt="issue when creating an S3 bucket on AWS" width="1027" height="234">
<ul>
<li>Reinitialize the workspace:</li>
</ul>
<pre class="language-yaml"><code>terraform init</code></pre>
<blockquote data-start="964" data-end="1045">
This initializes the backend and connects Terraform to the specified S3 bucket.
</blockquote>
Expected Output:
<pre class="language-yaml"><code>Initializing the backend...

Successfully configured the backend "s3"! Terraform will automatically
use this backend unless the backend configuration changes.
Initializing modules...
Initializing provider plugins...
- Reusing previous version of hashicorp/aws from the dependency lock file
- Using previously-installed hashicorp/aws v4.67.0

Terraform has been successfully initialized!
...</code></pre>
<ul>
<li>Then, run <code>terraform plan</code> to check for changes, followed by <code>terraform apply</code> to deploy the infrastructure.</li>
<li>After execution, verify in the S3 bucket that the <code>terraform.state</code> (<code>key</code>) file is stored in <code>terraform-learning-demo01</code>&nbsp;(<code>bucket</code>).</li>
</ul>
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://api.reliasoftware.com/uploads/terraform_learning_demo1_eb94605b8d.webp" alt="terraform-learning-demo01" width="923" height="357">
<ul>
<li>In the <code>.terraform/terraform.tfstate</code> directory, you will find the information of backend configuration. This confirms that we have successfully configured state storage on S3.</li>
</ul>
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://api.reliasoftware.com/uploads/information_of_backend_configuration_98e6834e9b.webp" alt="information of backend configuration" width="523" height="945">
<h3>State Locking</h3>
S3 State Locking
<ul>
<li>To enable S3 state locking, add the <code>use_lockfile</code> parameter (only available in Terraform 1.10+) to the <code>backend</code> block. The <code>main.tf</code> file now looks like this:</li>
</ul>
<pre class="language-yaml"><code>terraform {
 backend "s3" {
 bucket = "terraform-learning-demo01"
 key = "terraform.tfstate"
 region = "us-east-1"
 profile = "saa"
 use_lockfile = true
 }

 ...
}
...</code></pre>
<ul>
<li>Modify a resource value (e.g., the subnet CIDR block) and run <code>terraform apply</code> simultaneously. You will see an error in the console:</li>
</ul>
<img src="https://api.reliasoftware.com/uploads/error_in_the_console_081bbe292e.webp" alt="error in the console" width="1184" height="337">
<ul>
<li>A lock file <code>{key}.tflock</code> appears in the S3 bucket, preventing simultaneous apply operations:</li>
</ul>
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://api.reliasoftware.com/uploads/a_lock_file_in_the_s3_bucket_aa64a851ff.webp" alt="A lock file {key}.tflock appears in the S3 bucket" width="1019" height="216">
<ul>
<li>Once the apply operation completes, the lock file is deleted, and the state file will be added in S3:</li>
</ul>
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://api.reliasoftware.com/uploads/the_state_file_will_be_added_in_s3_cbb45e46fe.webp" alt="the state file will be added in S3" width="1011" height="200">
<h3>DynamoDB State Locking</h3>
<ul>
<li>Create a DynamoDB table named <code>terraform-tfstate</code> with <code>LockID</code> as the partition key of type <code>string</code>.</li>
</ul>
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://api.reliasoftware.com/uploads/create_a_dynamodb_table_714b407032.webp" alt="Create a DynamoDB table" width="1111" height="395">
<ul>
<li>If not, this issue will appear:&nbsp;</li>
</ul>
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://api.reliasoftware.com/uploads/error_when_creating_a_dynamodb_table_7a26961c39.webp" alt="error when creating a DynamoDB table " width="803" height="216">
<ul>
<li>Configure DynamoDB in <code>main.tf</code>:</li>
</ul>
<pre class="language-yaml"><code>terraform {
 backend "s3" {
 bucket = "terraform-learning-demo01"
 key = "terraform.tfstate"
 region = "us-east-1"
 profile = "saa"
 dynamodb_table = "terraform-tfstate"
 }
}</code></pre>
<ul>
<li>Running <code>terraform apply</code> simultaneously will result in an error:</li>
</ul>
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://api.reliasoftware.com/uploads/error_when_running_terraform_apply_simultaneously_55547e32fa.webp" alt="Running terraform apply simultaneously will cause error" width="1112" height="320">
<ul>
<li>The DynamoDB table contains a record with <code>LockID</code> formatted as <code>{bucket}/{key}</code>.</li>
</ul>
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://api.reliasoftware.com/uploads/the_dynamodb_table_contains_a_record_with_lockid_fdce0fffad.webp" alt="The DynamoDB table contains a record with LockID" width="1200" height="186">
<ul>
<li>Once apply excecuted, file <code>state</code> will be created in <code>S3</code>:</li>
</ul>
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://api.reliasoftware.com/uploads/file_state_will_be_created_in_s3_a80e0d1a0c.webp" alt="file state will be created in S3" width="1102" height="302">
<ul>
<li>Once the process completes, the lock record is deleted, but a <code>{bucket}/{key}-md5</code> file is created:</li>
</ul>
<img style="display: block; margin-left: auto; margin-right: auto;" src="https://api.reliasoftware.com/uploads/a_bucket_key_md5_file_is_created_574e777434.webp" alt="a {bucket}/{key}-md5 file is created" width="755" height="153">
&gt;&gt; Explore: Top 20&nbsp;<a href="https://reliasoftware.com/blog/infrastructure-as-code-tools">Infrastructure as Code (IaC) Tools</a> For Businesses
<h2>Conclusion</h2>
<ul>
<li>Terraform provides the <code>backend</code> block to define state file storage locations.</li>
<li>Multiple backend options are available: <code>local</code>, <code>remote</code>, <code>s3</code>, etc.</li>
<li>The <code>s3</code> backend supports state locking via S3 native (Terraform 1.10+) or DynamoDB:
<ul>
<li>When applying changes, a <code>.lock</code> file is created in S3 or DynamoDB.</li>
<li>Once the process completes, the lock file is removed, and the state file is updated in S3.</li>
</ul>
</li>
</ul>
<div id="article_content" class="inner_article__entries__X3PKd">
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A Terraform backend defines how and where Terraform stores its state file (<code data-start="139" data-end="158">terraform.tfstate</code>). Terraform remote backends like S3 are used to solve conflicts.

What is Terraform Backend? Dive into Terraform Backend S3 | Relia Software

What is Terraform Backend? Dive into Terraform Backend S3

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