diff --git a/docs/roles/aws/aws_ec2_autoscale_cluster.md b/docs/roles/aws/aws_ec2_autoscale_cluster.md
index 5e6909609..49f419391 100644
--- a/docs/roles/aws/aws_ec2_autoscale_cluster.md
+++ b/docs/roles/aws/aws_ec2_autoscale_cluster.md
@@ -36,6 +36,8 @@ aws_ec2_autoscale_cluster:
   vpc_id: vpc-XXXX # One of vpc_id or vpc_name is mandatory.
   # vpc_name: example-vpc
   subnets:
+    # If rds.rds.true is set and you are creating an RDS instance then you must use at least two AZs, this is hard requirement.
+    # This means your region and environment must also have a minimum of two subnets - see `aws_vpc_subnet`
     # - az: a
     #   cidr: "10.0.3.0/26"
     - az: b
diff --git a/docs/roles/aws/aws_rds.md b/docs/roles/aws/aws_rds.md
index e89cd6e74..1e5287a15 100644
--- a/docs/roles/aws/aws_rds.md
+++ b/docs/roles/aws/aws_rds.md
@@ -19,6 +19,7 @@ aws_rds:
   aws_profile: "{{ _aws_profile }}"
   region: "{{ _aws_region }}"
   multi_az: true
+  # You must provide at least two subnets in two different AZs, even for single AZ deployments.
   subnets:
     - subnet-aaaaaaaa
     - subnet-bbbbbbbb
diff --git a/docs/roles/aws/aws_vpc_subnet.md b/docs/roles/aws/aws_vpc_subnet.md
index 5d97d303a..1b4ef012b 100644
--- a/docs/roles/aws/aws_vpc_subnet.md
+++ b/docs/roles/aws/aws_vpc_subnet.md
@@ -11,6 +11,7 @@ aws_vpc_subnet:
   # vpc_name: example-vpc
   aws_profile: "{{ _aws_profile }}"
   region: "{{ _aws_region }}"
+  # If you intend to have RDS instances you must provide at least two subnets.
   subnets:
     - cidr_block: "10.0.0.0/24"
       # ipv6_cidr_block: "1" # This will create something like xxxx:xxxx:xxxx:xxyy::/64 where yy is created using the ansible.utils.ipsubnet filter automatically - DO NOT DEFINE IF IPV6 IS NOT REQUIRED
diff --git a/roles/aws/aws_ec2_autoscale_cluster/README.md b/roles/aws/aws_ec2_autoscale_cluster/README.md
index 5e6909609..49f419391 100644
--- a/roles/aws/aws_ec2_autoscale_cluster/README.md
+++ b/roles/aws/aws_ec2_autoscale_cluster/README.md
@@ -36,6 +36,8 @@ aws_ec2_autoscale_cluster:
   vpc_id: vpc-XXXX # One of vpc_id or vpc_name is mandatory.
   # vpc_name: example-vpc
   subnets:
+    # If rds.rds.true is set and you are creating an RDS instance then you must use at least two AZs, this is hard requirement.
+    # This means your region and environment must also have a minimum of two subnets - see `aws_vpc_subnet`
     # - az: a
     #   cidr: "10.0.3.0/26"
     - az: b
diff --git a/roles/aws/aws_ec2_autoscale_cluster/defaults/main.yml b/roles/aws/aws_ec2_autoscale_cluster/defaults/main.yml
index 5bdd39aef..9af962f5c 100644
--- a/roles/aws/aws_ec2_autoscale_cluster/defaults/main.yml
+++ b/roles/aws/aws_ec2_autoscale_cluster/defaults/main.yml
@@ -17,6 +17,8 @@ aws_ec2_autoscale_cluster:
   vpc_id: vpc-XXXX # One of vpc_id or vpc_name is mandatory.
   # vpc_name: example-vpc
   subnets:
+    # If rds.rds.true is set and you are creating an RDS instance then you must use at least two AZs, this is hard requirement.
+    # This means your region and environment must also have a minimum of two subnets - see `aws_vpc_subnet`
     # - az: a
     #   cidr: "10.0.3.0/26"
     - az: b
diff --git a/roles/aws/aws_rds/README.md b/roles/aws/aws_rds/README.md
index e89cd6e74..1e5287a15 100644
--- a/roles/aws/aws_rds/README.md
+++ b/roles/aws/aws_rds/README.md
@@ -19,6 +19,7 @@ aws_rds:
   aws_profile: "{{ _aws_profile }}"
   region: "{{ _aws_region }}"
   multi_az: true
+  # You must provide at least two subnets in two different AZs, even for single AZ deployments.
   subnets:
     - subnet-aaaaaaaa
     - subnet-bbbbbbbb
diff --git a/roles/aws/aws_rds/defaults/main.yml b/roles/aws/aws_rds/defaults/main.yml
index 96b4d4914..faa3ee5bb 100644
--- a/roles/aws/aws_rds/defaults/main.yml
+++ b/roles/aws/aws_rds/defaults/main.yml
@@ -2,6 +2,7 @@ aws_rds:
   aws_profile: "{{ _aws_profile }}"
   region: "{{ _aws_region }}"
   multi_az: true
+  # You must provide at least two subnets in two different AZs, even for single AZ deployments.
   subnets:
     - subnet-aaaaaaaa
     - subnet-bbbbbbbb
diff --git a/roles/aws/aws_vpc_subnet/README.md b/roles/aws/aws_vpc_subnet/README.md
index 5d97d303a..1b4ef012b 100644
--- a/roles/aws/aws_vpc_subnet/README.md
+++ b/roles/aws/aws_vpc_subnet/README.md
@@ -11,6 +11,7 @@ aws_vpc_subnet:
   # vpc_name: example-vpc
   aws_profile: "{{ _aws_profile }}"
   region: "{{ _aws_region }}"
+  # If you intend to have RDS instances you must provide at least two subnets.
   subnets:
     - cidr_block: "10.0.0.0/24"
       # ipv6_cidr_block: "1" # This will create something like xxxx:xxxx:xxxx:xxyy::/64 where yy is created using the ansible.utils.ipsubnet filter automatically - DO NOT DEFINE IF IPV6 IS NOT REQUIRED
diff --git a/roles/aws/aws_vpc_subnet/defaults/main.yml b/roles/aws/aws_vpc_subnet/defaults/main.yml
index 1e29a7d01..e72b3ae64 100644
--- a/roles/aws/aws_vpc_subnet/defaults/main.yml
+++ b/roles/aws/aws_vpc_subnet/defaults/main.yml
@@ -3,6 +3,7 @@ aws_vpc_subnet:
   # vpc_name: example-vpc
   aws_profile: "{{ _aws_profile }}"
   region: "{{ _aws_region }}"
+  # If you intend to have RDS instances you must provide at least two subnets.
   subnets:
     - cidr_block: "10.0.0.0/24"
       # ipv6_cidr_block: "1" # This will create something like xxxx:xxxx:xxxx:xxyy::/64 where yy is created using the ansible.utils.ipsubnet filter automatically - DO NOT DEFINE IF IPV6 IS NOT REQUIRED