website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
---
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page_title: Modules - Configuration Language
description: >-
Modules are containers for multiple resources that are used together in
configurations. Learn how to call one module from another and access module
output.
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
---
# Module Blocks
> **Hands-on:** Try the [Reuse Configuration with Modules](https://learn.hashicorp.com/collections/terraform/modules?utm_source=WEBSITE&utm_medium=WEB_IO&utm_offer=ARTICLE_PAGE&utm_content=DOCS) collection on HashiCorp Learn.
A _module_ is a container for multiple resources that are used together.
Every Terraform configuration has at least one module, known as its
_root module_, which consists of the resources defined in the `.tf` files in
the main working directory.
A module can call other modules, which lets you include the child module's
resources into the configuration in a concise way. Modules
can also be called multiple times, either within the same configuration or
in separate configurations, allowing resource configurations to be packaged
and re-used.
This page describes how to call one module from another. For more information
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about creating re-usable child modules, see [Module Development](/language/modules/develop).
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
## Calling a Child Module
To _call_ a module means to include the contents of that module into the
configuration with specific values for its
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[input variables](/language/values/variables). Modules are called
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
from within other modules using `module` blocks:
```hcl
module "servers" {
source = "./app-cluster"
servers = 5
}
```
A module that includes a `module` block like this is the _calling module_ of the
child module.
The label immediately after the `module` keyword is a local name, which the
calling module can use to refer to this instance of the module.
Within the block body (between `{` and `}`) are the arguments for the module.
Module calls use the following kinds of arguments:
- The `source` argument is mandatory for all modules.
- The `version` argument is recommended for modules from a registry.
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- Most other arguments correspond to [input variables](/language/values/variables)
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
defined by the module. (The `servers` argument in the example above is one of
these.)
- Terraform defines a few other meta-arguments that can be used with all
modules, including `for_each` and `depends_on`.
### Source
All modules **require** a `source` argument, which is a meta-argument defined by
Terraform. Its value is either the path to a local directory containing the
module's configuration files, or a remote module source that Terraform should
download and use. This value must be a literal string with no template
sequences; arbitrary expressions are not allowed. For more information on
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possible values for this argument, see [Module Sources](/language/modules/sources).
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
The same source address can be specified in multiple `module` blocks to create
multiple copies of the resources defined within, possibly with different
variable values.
After adding, removing, or modifying `module` blocks, you must re-run
`terraform init` to allow Terraform the opportunity to adjust the installed
modules. By default this command will not upgrade an already-installed module;
use the `-upgrade` option to instead upgrade to the newest available version.
### Version
When using modules installed from a module registry, we recommend explicitly
constraining the acceptable version numbers to avoid unexpected or unwanted
changes.
Use the `version` argument in the `module` block to specify versions:
```shell
module "consul" {
source = "hashicorp/consul/aws"
version = "0.0.5"
servers = 3
}
```
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The `version` argument accepts a [version constraint string](/language/expressions/version-constraints).
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
Terraform will use the newest installed version of the module that meets the
constraint; if no acceptable versions are installed, it will download the newest
version that meets the constraint.
Version constraints are supported only for modules installed from a module
registry, such as the public [Terraform Registry](https://registry.terraform.io/)
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or [Terraform Cloud's private module registry](/cloud-docs/registry).
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
Other module sources can provide their own versioning mechanisms within the
source string itself, or might not support versions at all. In particular,
modules sourced from local file paths do not support `version`; since
they're loaded from the same source repository, they always share the same
version as their caller.
### Meta-arguments
Along with `source` and `version`, Terraform defines a few more
optional meta-arguments that have special meaning across all modules,
described in more detail in the following pages:
- `count` - Creates multiple instances of a module from a single `module` block.
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See [the `count` page](/language/meta-arguments/count)
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
for details.
- `for_each` - Creates multiple instances of a module from a single `module`
block. See
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[the `for_each` page](/language/meta-arguments/for_each)
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
for details.
- `providers` - Passes provider configurations to a child module. See
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[the `providers` page](/language/meta-arguments/module-providers)
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
for details. If not specified, the child module inherits all of the default
(un-aliased) provider configurations from the calling module.
- `depends_on` - Creates explicit dependencies between the entire
module and the listed targets. See
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[the `depends_on` page](/language/meta-arguments/depends_on)
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
for details.
In addition to the above, the `lifecycle` argument is not currently used by
Terraform but is reserved for planned future features.
## Accessing Module Output Values
The resources defined in a module are encapsulated, so the calling module
cannot access their attributes directly. However, the child module can
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declare [output values](/language/values/outputs) to selectively
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
export certain values to be accessed by the calling module.
For example, if the `./app-cluster` module referenced in the example above
exported an output value named `instance_ids` then the calling module
can reference that result using the expression `module.servers.instance_ids`:
```hcl
resource "aws_elb" "example" {
# ...
instances = module.servers.instance_ids
}
```
For more information about referring to named values, see
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[Expressions](/language/expressions).
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
## Transferring Resource State Into Modules
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Moving `resource` blocks from one module into several child modules causes
Terraform to see the new location as an entirely different resource. As a
result, Terraform plans to destroy all resource instances at the old address
and create new instances at the new address.
To preserve existing objects, you can use
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[refactoring blocks](/language/modules/develop/refactoring) to record the old and new
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addresses for each resource instance. This directs Terraform to treat existing
objects at the old addresses as if they had originally been created at the
corresponding new addresses.
## Replacing resources within a module
You may have an object that needs to be replaced with a new object for a reason
that isn't automatically visible to Terraform, such as if a particular virtual
machine is running on degraded underlying hardware. In this case, you can use
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[the `-replace=...` planning option](/cli/commands/plan#replace-address)
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to force Terraform to propose replacing that object.
If the object belongs to a resource within a nested module, specify the full
path to that resource including all of the nested module steps leading to it.
For example:
```shellsession
$ terraform plan -replace=module.example.aws_instance.example
website: Break up main Modules and Module Development pages
This one is a lot like the previous two commits, but slightly more complex:
- Only adding one new meta-argument page, for `providers`; otherwise, it just
re-uses the dual-purpose pages I made in the resources commit.
- About that `providers` argument: The stuff that was relevant to consumers of a
module went in that meta-argument page, but there was also a huge deep dive on
how the _author_ of a re-usable module should handle provider configurations
in cases where inheriting the default providers isn't sufficient. THAT, I
moved into a new page in the module development section. (For the consumer of
a module, this should all be an implementation detail; the module README
should tell you which aliased providers you need to configure and pass, and
then you just do it, without worrying about proxy configuration blocks etc.)
- The "standard module structure" recommendations in the main module development
page gets a page of its own, to make it more prominent and discoverable.
- Same deal with using the old URL as a landing page, at least for the main
module calls page. It didn't seem necessary for the module development page.
2020-11-13 03:21:35 +01:00
```
2021-07-09 01:58:26 +02:00
The above selects a `resource "aws_instance" "example"` declared inside a
`module "example"` child module declared inside your root module.
Because replacing is a very disruptive action, Terraform only allows selecting
individual resource instances. There is no syntax to force replacing _all_
resource instances belonging to a particular module.
