Remove redundand security group rules

I wrongly assummed that they work like a firewall rules and I thought if
we make a request to particular port from random port we need to allow
connections back. It's not true. It seems security group rules are
applied to connection creation not to literal data flow.

Author: dzhlobo

aws/mysql/mysql.tf

@@ -117,18 +117,6 @@ resource "aws_security_group_rule" "db_ingress" {
   source_security_group_id = each.value
 }
 
-resource "aws_security_group_rule" "db_egress" {
-  for_each = toset(var.allow_security_group_ids)
-
-  security_group_id = aws_security_group.database.id
-  description = "Egress from mysql"
-  type = "egress"
-  protocol = "tcp"
-  from_port = 0
-  to_port = 0
-  source_security_group_id = each.value
-}
-
 resource "aws_security_group_rule" "egress_to_db" {
   for_each = toset(var.allow_security_group_ids)
 
@@ -141,18 +129,6 @@ resource "aws_security_group_rule" "egress_to_db" {
   source_security_group_id = aws_security_group.database.id
 }
 
-resource "aws_security_group_rule" "ingress_from_db" {
-  for_each = toset(var.allow_security_group_ids)
-
-  security_group_id = each.value
-  description = "Ingress from mysql"
-  type = "ingress"
-  protocol = "tcp"
-  from_port = 0
-  to_port = 0
-  source_security_group_id = aws_security_group.database.id
-}
-
 resource "random_password" "database" {
   length = 20
   special = true

aws/postgresql/postgresql.tf

@@ -117,18 +117,6 @@ resource "aws_security_group_rule" "db_ingress" {
   source_security_group_id = each.value
 }
 
-resource "aws_security_group_rule" "db_egress" {
-  for_each = toset(var.allow_security_group_ids)
-
-  security_group_id = aws_security_group.database.id
-  description = "Egress from PostgreSQL"
-  type = "egress"
-  protocol = "tcp"
-  from_port = 0
-  to_port = 0
-  source_security_group_id = each.value
-}
-
 resource "aws_security_group_rule" "egress_to_db" {
   for_each = toset(var.allow_security_group_ids)
 
@@ -141,18 +129,6 @@ resource "aws_security_group_rule" "egress_to_db" {
   source_security_group_id = aws_security_group.database.id
 }
 
-resource "aws_security_group_rule" "ingress_from_db" {
-  for_each = toset(var.allow_security_group_ids)
-
-  security_group_id = each.value
-  description = "Ingress from PostgreSQL"
-  type = "ingress"
-  protocol = "tcp"
-  from_port = 0
-  to_port = 0
-  source_security_group_id = aws_security_group.database.id
-}
-
 resource "random_password" "database" {
   length = 20
   special = true

aws/redis/redis.tf

@@ -82,18 +82,6 @@ resource "aws_security_group_rule" "redis_ingress" {
   source_security_group_id = each.value
 }
 
-resource "aws_security_group_rule" "redis_egress" {
-  for_each = toset(var.allow_security_group_ids)
-
-  security_group_id = aws_security_group.redis.id
-  description = "Egress from redis"
-  type = "egress"
-  protocol = "tcp"
-  from_port = 0
-  to_port = 0
-  source_security_group_id = each.value
-}
-
 resource "aws_security_group_rule" "egress_to_redis" {
   for_each = toset(var.allow_security_group_ids)
 
@@ -106,18 +94,6 @@ resource "aws_security_group_rule" "egress_to_redis" {
   source_security_group_id = aws_security_group.redis.id
 }
 
-resource "aws_security_group_rule" "ingress_from_redis" {
-  for_each = toset(var.allow_security_group_ids)
-
-  security_group_id = each.value
-  description = "Ingress from redis"
-  type = "ingress"
-  protocol = "tcp"
-  from_port = 0
-  to_port = 0
-  source_security_group_id = aws_security_group.redis.id
-}
-
 output "host" {
   value = aws_elasticache_cluster.redis.cache_nodes.0.address
 }