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WordPlumblr allows its users to use custom domains that point to the WordPlumblr infrastructure

A CNAME is an alias. It allows one domain to point to another domain which, eventually if you follow the CNAME chain, will resolve to an A record and IP address.

For example, WordPlumblr might have assigned the CNAME 6equj5.wordplumblr.com for Foo.com. Foo.com and the other customers may have all initially resolved, at the end of the CNAME chain, to the same IP address.

you usually don't want to address memory directly but, instead, you set up a pointer to a block of memory where you're going to store something. If the operating system needs to move the memory around then it just updates the pointer to point to wherever the chunk of memory has been moved to.

the DNS spec enshrined that the root record -- the naked domain without any subdomain -- could not be a CNAME.

a way to support a CNAME at the root, but still follow the RFC and return an IP address for any query for the root record.

extended our authoritative DNS infrastructure to, in certain cases, act as a kind of DNS resolver.

allows the flexibility of having CNAMEs at the root without breaking the DNS specification.

We cache the CNAME responses -- respecting the DNS TTLs, just like a recursor should -- which means often we have the answer without having to traverse the chain.

CNAME flattening solved email resolution errors for us which was very key.

After the block type keyword and any labels, the block body is delimited by the { and } characters

Identifiers can contain letters, digits, underscores (_), and hyphens (-). The first character of an identifier must not be a digit, to avoid ambiguity with literal numbers.

The # single-line comment style is the default comment style and should be used in most cases.

he idiomatic style is to use the Unix convention

Indent two spaces for each nesting level.

align their equals signs

Use empty lines to separate logical groups of arguments within a block.

Use one blank line to separate the arguments from the blocks.

"meta-arguments" (as defined by the Terraform language semantics)

Avoid separating multiple blocks of the same type with other blocks of a different type, unless the block types are defined by semantics to form a family.

Resource names must start with a letter or underscore, and may contain only letters, digits, underscores, and dashes.

By convention, resource type names start with their provider's preferred local name.

Most publicly available providers are distributed on the Terraform Registry, which also hosts their documentation.

The Terraform language defines several meta-arguments, which can be used with any resource type to change the behavior of resources.

use precondition and postcondition blocks to specify assumptions and guarantees about how the resource operates.

Some resource types provide a special timeouts nested block argument that allows you to customize how long certain operations are allowed to take before being considered to have failed.

Timeouts are handled entirely by the resource type implementation in the provider

Most resource types do not support the timeouts block at all.

A resource block declares that you want a particular infrastructure object to exist with the given settings.

Destroy resources that exist in the state but no longer exist in the configuration.

Destroy and re-create resources whose arguments have changed but which cannot be updated in-place due to remote API limitations.

Expressions within a Terraform module can access information about resources in the same module, and you can use that information to help configure other resources. Use the <RESOURCE TYPE>.<NAME>.<ATTRIBUTE> syntax to reference a resource attribute in an expression.

resources often provide read-only attributes with information obtained from the remote API; this often includes things that can't be known until the resource is created, like the resource's unique random ID.

data sources, which are a special type of resource used only for looking up information.

some dependencies cannot be recognized implicitly in configuration.

local-only resource types exist for generating private keys, issuing self-signed TLS certificates, and even generating random ids.

The count meta-argument accepts a whole number, and creates that many instances of the resource or module.

the count value must be known before Terraform performs any remote resource actions. This means count can't refer to any resource attributes that aren't known until after a configuration is applied

Within nested provisioner or connection blocks, the special self object refers to the current resource instance, not the resource block as a whole.