Feature/practice19

04-Terraform-Variables-and-Datasources/terraform-manifests/c5-ec2instance.tf

@@ -9,3 +9,6 @@ resource "aws_instance" "myec2vm" {
     "Name" = "EC2 Demo 2"
   }
 }
+
+
+

Vikram-Notes.md

@@ -0,0 +1,413 @@
+=========================SUPERNOTES==============================================
+>understand block, argument and attribute
+
+>.\terraform destroy -target="aws_instance.my-ec2-instance"
+
+>for list variable use variable "aws_instance_type_list" and same for map with string
+
+>if used count the update output to list output for each instance like value = [for instance in aws_instance.my-ec2-instance : instance.public_ip]
+
+>understand difference between user_data (bootstrp) and datasource (data)
+user_data = file("${path.module}/app1-install.sh")
+# Create a datasource to fetch the Latest Linux AMI ID for the specified region and name
+data "aws_ami" "latest_linux_ami" { # data.aws_ami.latest_linux_ami.id
+
+>`for_each` Meta-Argument # for_each only works with map or set
+- `toset` function
+- `tomap` function
+
+>var.<list_name>[<index>]
+ar.instance_type_list[1]  # => "t3.small"
+
+>var.instance_type_list[1]  # => "t3.small"
+var.<map_name>["<key>"]
+
+>output "<name>" {
+  value = [for <item> in <resource> : <item>.<attribute>]
+output "for_output_list" {
+  value = [for instance in aws_instance.myec2vm : instance.public_dns]
+
+>output "<name>" {
+  value = {for <item> in <resource> : <key_expr> => <value_expr>}
+output "for_output_map1" {
+  value = {for instance in aws_instance.myec2vm : instance.id => instance.public_dns}
+
+>resource "aws_instance" "myec2vm" {
+  ami           = data.aws_ami.amzlinux2.id
+  instance_type = var.instance_type
+  key_name      = var.instance_keypair
+
+  for_each = toset(data.aws_availability_zones.available.names)
+  availability_zone = each.key
+
+  tags = {
+    Name = "For-Each-Demo-${each.key}"
+  }
+}
+
+>for_each only works with map or set
+
+
+
+
+
+
+=====================================================================================
+
+count Meta-Argument — Easy Formula
+✅ Easy-to-Remember Formula:
+
+resource "<type>" "<name>" {
+  count = <number>
+  # other resource config
+  tags = {
+    Name = "<custom-name-prefix>${count.index}"
+  }
+}
+
+🔁 Plug in:
+
+    <type> = aws_instance
+
+    <name> = myec2vm
+
+    <number> = 2
+
+    <custom-name-prefix> = "Count-Demo-"
+
+✅ Final Code:
+
+resource "aws_instance" "myec2vm" {
+  count         = 2
+  instance_type = "t3.micro"
+  tags = {
+    Name = "Count-Demo-${count.index}"
+  }
+}
+
+🧠 Remember:
+
+    count = how many copies
+
+    count.index = 0, 1, 2... use for naming
+
+📃 List & Map Variable Access — Easy Formula
+✅ List Access Formula:
+
+var.<list_name>[<index>]
+
+Example:
+
+var.instance_type_list[1]  # => "t3.small"
+
+✅ Map Access Formula:
+
+var.<map_name>["<key>"]
+
+Example:
+
+var.instance_type_map["prod"]  # => "t3.large"
+
+🧠 Remember:
+
+    Lists = ordered → use numbers
+
+    Maps = named → use keys
+
+🔁 For Loop with List — Easy Formula
+✅ Easy-to-Remember Formula:
+
+output "<name>" {
+  value = [for <item> in <resource> : <item>.<attribute>]
+}
+
+🔁 Plug in:
+
+    <name> = for_output_list
+
+    <item> = instance
+
+    <resource> = aws_instance.myec2vm
+
+    <attribute> = public_dns
+
+✅ Final Code:
+
+output "for_output_list" {
+  value = [for instance in aws_instance.myec2vm : instance.public_dns]
+}
+
+🔁 For Loop with Map — Easy Formula
+✅ Easy-to-Remember Formula:
+
+output "<name>" {
+  value = {for <item> in <resource> : <key_expr> => <value_expr>}
+}
+
+🔁 Plug in:
+
+    <name> = for_output_map1
+
+    <item> = instance
+
+    <resource> = aws_instance.myec2vm
+
+    <key_expr> = instance.id
+
+    <value_expr> = instance.public_dns
+
+✅ Final Code:
+
+output "for_output_map1" {
+  value = {for instance in aws_instance.myec2vm : instance.id => instance.public_dns}
+}
+
+🔁 For Loop with Map – Advanced
+✅ Formula:
+
+output "<name>" {
+  value = {for <key>, <value> in <resource> : <key> => <value>.<attribute>}
+}
+
+Plug in:
+
+    <name> = for_output_map2
+
+    <key> = c
+
+    <value> = instance
+
+    <attribute> = public_dns
+
+✅ Final Code:
+
+output "for_output_map2" {
+  value = {for c, instance in aws_instance.myec2vm : c => instance.public_dns}
+}
+
+💥 Splat Operator — Easy Formula
+✅ Legacy:
+
+<resource>.*.<attribute>
+
+✅ Modern (Preferred):
+
+<resource>[*].<attribute>
+
+Example:
+
+aws_instance.myec2vm[*].public_dns
+
+🧠 Remember:
+
+    [*].attr = grab all values of attr from multiple resources
+
+🌐 For-Each EC2 per AZ with toset — Easy Formula
+✅ for_each Formula:
+
+resource "<type>" "<name>" {
+  for_each = toset(<list>)
+  availability_zone = each.key
+}
+
+Plug in:
+
+    <type> = aws_instance
+
+    <name> = myec2vm
+
+    <list> = data.aws_availability_zones.my_azones.names
+
+✅ Final Code:
+
+resource "aws_instance" "myec2vm" {
+  for_each = toset(data.aws_availability_zones.my_azones.names)
+  availability_zone = each.key
+}
+
+📤 Output with toset() — Easy Formula
+✅ Formula:
+
+output "<name>" {
+  value = toset([for <item> in <resource> : <item>.<attribute>])
+}
+
+Plug in:
+
+    <name> = instance_publicip
+
+    <item> = myec2vm
+
+    <resource> = aws_instance.myec2vm
+
+    <attribute> = public_ip
+
+✅ Final Code:
+
+output "instance_publicip" {
+  value = toset([for myec2vm in aws_instance.myec2vm : myec2vm.public_ip])
+}
+
+🗺️ Output with tomap() — Easy Formula
+✅ Formula:
+
+output "<name>" {
+  value = tomap({
+    for <key>, <value> in <resource> : <key> => <value>.<attribute>
+  })
+}
+
+Plug in:
+
+    <name> = instance_publicdns2
+
+    <key> = s
+
+    <value> = myec2vm
+
+    <attribute> = public_dns
+
+✅ Final Code:
+
+output "instance_publicdns2" {
+  value = tomap({
+    for s, myec2vm in aws_instance.myec2vm : s => myec2vm.public_dns
+  })
+}
+
+🧠 TL;DR Summary Table
+Formula Type	Template
+count Resource	count = <number> + "${count.index}" for unique names
+List Access	var.<list>[<index>]
+Map Access	var.<map>["<key>"]
+For Loop (List)	[for <x> in <resource> : <x>.<attribute>]
+For Loop (Map)	{for <x> in <resource> : <key> => <value>}
+Advanced Map Loop	{for <k>, <v> in <resource> : <k> => <v>.<attr>}
+Splat (Modern)	<resource>[*].<attribute>
+for_each with set	for_each = toset(<list>) + each.key
+Output with toset()	toset([for <x> in <res> : <x>.<attr>])
+Output with tomap()	tomap({for <k>, <v> in <res> : <k> => <v>.<attr>})
+
+for_each in Terraform — Easy-to-Remember Formula 💡
+✅ Basic for_each Formula (with set or map)
+
+resource "<type>" "<name>" {
+  for_each = <collection>  # toset(...) or map
+
+  <some_property> = each.key
+  # OR
+  <some_property> = each.value
+
+  tags = {
+    Name = "<prefix>-${each.key}"  # great for naming
+  }
+}
+
+✅ Example 1: for_each with Set (using toset())
+📦 Goal: Create one EC2 instance per Availability Zone
+Step-by-Step Plug-In:
+
+    <type> = aws_instance
+
+    <name> = myec2vm
+
+    <collection> = toset(data.aws_availability_zones.available.names)
+
+    <some_property> = availability_zone
+
+    <prefix> = For-Each-Demo
+
+✅ Final Code:
+
+resource "aws_instance" "myec2vm" {
+  ami           = data.aws_ami.amzlinux2.id
+  instance_type = var.instance_type
+  key_name      = var.instance_keypair
+
+  for_each = toset(data.aws_availability_zones.available.names)
+  availability_zone = each.key
+
+  tags = {
+    Name = "For-Each-Demo-${each.key}"
+  }
+}
+
+✅ Example 2: for_each with Map
+📦 Goal: Launch different EC2 instances per environment
+
+variable "env_map" {
+  default = {
+    dev  = "t3.micro"
+    prod = "t3.large"
+  }
+}
+
+Step-by-Step Plug-In:
+
+    <type> = aws_instance
+
+    <name> = env_instance
+
+    <collection> = var.env_map
+
+    <some_property> = instance_type = each.value
+
+    <prefix> = Env-VM
+
+✅ Final Code:
+
+resource "aws_instance" "env_instance" {
+  ami           = data.aws_ami.amzlinux2.id
+  instance_type = each.value
+  key_name      = var.instance_keypair
+
+  for_each = var.env_map
+
+  tags = {
+    Name = "Env-VM-${each.key}"
+  }
+}
+
+✅ Output with for_each — Use in Combination
+🧾 Formula:
+
+output "<name>" {
+  value = toset([
+    for <item> in <resource> : <item>.<attribute>
+  ])
+}
+
+✅ Map Output with tomap():
+
+output "<name>" {
+  value = tomap({
+    for <key>, <item> in <resource> : <key> => <item>.<attribute>
+  })
+}
+
+🧠 Quick Reference Table
+Part	Formula / Meaning
+for_each = toset(<list>)	Use when you have a list
+for_each = <map>	Use when you want key-value pairing
+each.key	Current key (like AZ name or env name)
+each.value	Value from the map (like instance type)
+Use in tags	"Name" = "prefix-${each.key}"
+toset([...])	Convert list of items to a set for output
+tomap({...})	Convert looped values to a map for output
+🎯 Mnemonic to Remember
+
+    "For Each Thing, Do a Unique Thing!"
+    Use each.key for naming, each.value for config.
+
+✅ TL;DR Template
+
+resource "<type>" "<name>" {
+  for_each = toset(<list>)  # or just a map
+
+  <some_property> = each.key  # or each.value
+
+  tags = {
+    Name = "<prefix>-${each.key}"
+  }
+}
+