My Lambda can't connect to my RDS instance - amazon-web-services

Question

I'm trying to create both services within the same VPC and give them appropriate security groups but they I can't make it work.
variable "vpc_cidr_block" {
default = "10.1.0.0/16"
}
variable "cidr_block_subnet_public" {
default = "10.1.1.0/24"
}
variable "cidr_block_subnets_private" {
default = ["10.1.2.0/24", "10.1.3.0/24", "10.1.4.0/24"]
}
data "aws_availability_zones" "available" {
state = "available"
}
resource "aws_vpc" "vpc" {
cidr_block = var.vpc_cidr_block
}
resource "aws_subnet" "private" {
count = length(var.cidr_block_subnets_private)
cidr_block = var.cidr_block_subnets_private[count.index]
vpc_id = aws_vpc.vpc.id
availability_zone = data.aws_availability_zones.available.names[count.index]
}
resource "aws_security_group" "lambda" {
vpc_id = aws_vpc.vpc.id
egress {
from_port = 0
to_port = 0
protocol = "-1"
cidr_blocks = ["0.0.0.0/0"]
}
}
resource "aws_security_group" "rds" {
vpc_id = aws_vpc.vpc.id
ingress {
description = "PostgreSQL"
from_port = 5432
protocol = "tcp"
to_port = 5432
// security_groups = [aws_security_group.lambda.id]
}
egress {
from_port = 0
to_port = 0
protocol = "-1"
cidr_blocks = ["0.0.0.0/0"]
}
}
resource "aws_lambda_function" "event" {
function_name = "ServerlessExampleEvent"
timeout = 30
s3_bucket = "mn-lambda"
s3_key = "mn/v1.0.0/lambda-1.0.0-all.jar"
handler = "dk.fitfit.handler.EventRequestHandler"
runtime = "java11"
memory_size = 256
role = aws_iam_role.event.arn
vpc_config {
security_group_ids = [aws_security_group.lambda.id]
subnet_ids = [for s in aws_subnet.private: s.id]
}
environment {
variables = {
JDBC_DATABASE_URL = "jdbc:postgresql://${aws_db_instance.rds.address}:${aws_db_instance.rds.port}/${aws_db_instance.rds.identifier}"
DATABASE_USERNAME = aws_db_instance.rds.username
DATABASE_PASSWORD = aws_db_instance.rds.password
}
}
}
resource "aws_db_subnet_group" "db" {
subnet_ids = aws_subnet.private.*.id
}
resource "aws_db_instance" "rds" {
allocated_storage = 10
engine = "postgres"
engine_version = "11.5"
instance_class = "db.t2.micro"
username = "postgres"
password = random_password.password.result
skip_final_snapshot = true
apply_immediately = true
vpc_security_group_ids = [aws_security_group.rds.id]
db_subnet_group_name = aws_db_subnet_group.db.name
}
resource "random_password" "password" {
length = 32
special = false
}
I tried to not clutter the question by only posting the relevant part of my HCL. Please let me know if I missed anything important.

Answer 1

The biggest issue is the commented out security_groups parameter on the ingress block of the rds security group. Uncommenting that should then allow Postgresql traffic from the lambda security group:
resource "aws_security_group" "rds" {
vpc_id = aws_vpc.vpc.id
ingress {
description = "PostgreSQL"
from_port = 5432
protocol = "tcp"
to_port = 5432
security_groups = [aws_security_group.lambda.id]
}
egress {
from_port = 0
to_port = 0
protocol = "-1"
cidr_blocks = ["0.0.0.0/0"]
}
}
As well as that your JDBC string is basically resolving to something like jdbc:postgresql://terraform-20091110230000000000000001.xxxx.us-east-1.rds.amazonaws.com:5432/terraform-20091110230000000000000001 because you aren't specifying an identifier for the RDS instance and so it defaults to generating an identifier prefixed with terraform- plus the timestamp and a counter. The important part to note here is that your RDS instance doesn't yet include a database of the name terraform-20091110230000000000000001 for your application to connect to because you haven't specified it.
You can have RDS create a database on the RDS instance by using the name parameter. You can then update your JDBC connection string to specify the database name as well:
resource "aws_db_instance" "rds" {
allocated_storage = 10
engine = "postgres"
engine_version = "11.5"
instance_class = "db.t2.micro"
username = "postgres"
password = random_password.password.result
skip_final_snapshot = true
apply_immediately = true
name = "foo"
vpc_security_group_ids = [aws_security_group.rds.id]
db_subnet_group_name = aws_db_subnet_group.db.name
}
resource "aws_lambda_function" "event" {
function_name = "ServerlessExampleEvent"
timeout = 30
s3_bucket = "mn-lambda"
s3_key = "mn/v1.0.0/lambda-1.0.0-all.jar"
handler = "dk.fitfit.handler.EventRequestHandler"
runtime = "java11"
memory_size = 256
role = aws_iam_role.event.arn
vpc_config {
security_group_ids = [aws_security_group.lambda.id]
subnet_ids = [for s in aws_subnet.private : s.id]
}
environment {
variables = {
JDBC_DATABASE_URL = "jdbc:postgresql://${aws_db_instance.rds.address}:${aws_db_instance.rds.port}/${aws_db_instance.rds.name}"
DATABASE_USERNAME = aws_db_instance.rds.username
DATABASE_PASSWORD = aws_db_instance.rds.password
}
}
}