Adding a pattern for common usage

docs/patterns.md

@@ -2,4 +2,138 @@
 
 Various usage patterns are prescribed below.
 
-<!-- TODO -->
+## Common Patterns
+There are several common patterns to use with the alb for example:              
+1. Redirect http to https               
+2. Configuring Instance Target Group           
+3. Return a fixed response              
+4. Create several security groups for the load balancer             
+5. Create a hosted zone record for the load balancer.           
+
+### Redirect http to https
+In the example below we can see a listener with that has a rule to redirect the requests.
+The nested blocks of `rules` define the different rules the listener will use. Notice this listener also redirects `http` to `https` before returning the response on the rule.
+`ex-http-https-redirect` -> `rules` -> `ex-fixed-response`
+```hcl
+...
+    ex-http-https-redirect = {
+      port     = 80
+      protocol = "HTTP"
+      redirect = {
+        port        = "443"
+        protocol    = "HTTPS"
+        status_code = "HTTP_301"
+      }
+
+      rules = {
+        ex-fixed-response = {
+          priority = 3
+          actions = [{
+            type         = "fixed-response"
+            content_type = "text/plain"
+            status_code  = 200
+            message_body = "This is a fixed response"
+          }]
+
+          conditions = [{
+            http_header = {
+              http_header_name = "x-Gimme-Fixed-Response"
+              values           = ["yes", "please", "right now"]
+            }
+          }]
+        }
+
+      }
+    }
+...
+```
+### Configuring Instance Target Group
+Each nested map defines a target group on the load balancer.                    
+The map allows the user to create several targets each with a unique name and the order will remain. In this example `instance_1` and `instance_2` are the target groups.
+
+```hcl
+target_groups = {
+    instance_1 = {
+      name_prefix                       = "h1"
+      backend_protocol                  = "HTTP"
+      backend_port                      = 80
+      target_type                       = "instance"
+      deregistration_delay              = 10
+      load_balancing_cross_zone_enabled = false
+    }
+    instance_2 = {
+      name_prefix                       = "h2"
+      backend_protocol                  = "HTTP"
+      backend_port                      = 80
+      target_type                       = "instance"
+      deregistration_delay              = 10
+      load_balancing_cross_zone_enabled = false
+    }
+
+}
+```
+### Fixed Response
+Each nested map defines a listener on the load balancer.                    
+The nested map below creates a listener with a fixed response of 200.
+`ex-fixed-response`->`fixed_response`                
+
+```hcl
+...
+listeners ={
+    ex-fixed-response = {
+      port     = 82
+      protocol = "HTTP"
+      fixed_response = {
+        content_type = "text/plain"
+        message_body = "Fixed message"
+        status_code  = "200"
+      }
+    }
+}
+...
+```
+### Security Groups
+Each nested map defines a securtiy group rule. The rules will be created by the module on the same security group
+notice we have in the example several nested maps:              
+* `security_group_ingress_rules`->`all_http`                
+* `security_group_ingress_rules`->`all_https`  
+```hcl
+...
+security_group_ingress_rules = {
+    all_http = {
+      from_port   = 80
+      to_port     = 80
+      ip_protocol = "tcp"
+      description = "HTTP web traffic"
+      cidr_ipv4   = "0.0.0.0/0"
+    }
+    all_https = {
+      from_port   = 443
+      to_port     = 443
+      ip_protocol = "tcp"
+      description = "HTTPS web traffic"
+      cidr_ipv4   = "0.0.0.0/0"
+    }
+  }
+...
+```
+### Hosted Zone
+Each nested map defines a route53 record.                    
+* `A` -> will be an A record and 
+* `AAAA` -> will be an AAAA record and 
+```hcl
+...
+  route53_records = {
+    A = {
+      name    = local.name
+      type    = "A"
+      zone_id = data.aws_route53_zone.this.id
+    }
+    AAAA = {
+      name    = local.name
+      type    = "AAAA"
+      zone_id = data.aws_route53_zone.this.id
+    }
+  }
+...
+```