[Terraform's RDS support](https://www.terraform.io/docs/providers/aws/r/db_instance.html) makes it easy to create a database instance. Here's a cheatsheet:

```
resource "aws_db_instance" "mydb1" {
  allocated_storage        = 256 # gigabytes
  backup_retention_period  = 7   # in days
  db_subnet_group_name     = "${var.rds_public_subnet_group}"
  engine                   = "postgres"
  engine_version           = "9.5.4"
  identifier               = "mydb1"
  instance_class           = "db.r3.large"
  multi_az                 = false
  name                     = "mydb1"
  parameter_group_name     = "mydbparamgroup1" # if you have tuned it
  password                 = "${trimspace(file("${path.module}/secrets/mydb1-password.txt"))}"
  port                     = 5432
  publicly_accessible      = true
  storage_encrypted        = true # you should always do this
  storage_type             = "gp2"
  username                 = "mydb1"
  vpc_security_group_ids   = ["${aws_security_group.mydb1.id}"]
}
```

Here's the security group you need:

```
resource "aws_security_group" "mydb1" {
  name = "mydb1"

  description = "RDS postgres servers (terraform-managed)"
  vpc_id = "${var.rds_vpc_id}"

  # Only postgres in
  ingress {
    from_port = 5432
    to_port = 5432
    protocol = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  # Allow all outbound traffic.
  egress {
    from_port = 0
    to_port = 0
    protocol = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}
```

You can get these values from the EC2 console (don't forget them!):

```
variable "rds_vpc_id" {
  default = "vpc-XXXXXXXX"
  description = "Our default RDS virtual private cloud (rds_vpc)."
}

variable "rds_public_subnets" {
  default = "subnet-YYYYYYYY,subnet-YYYYYYYY,subnet-YYYYYYYY,subnet-YYYYYYYY"
  description = "The public subnets of our RDS VPC rds-vpc."
}

variable "rds_public_subnet_group" {
  default = "default-vpc-XXXXXXXX"
  description = "Apparently the group name, according to the RDS launch wizard."
}
```

Check out our Terraform RDS cheatsheet that makes it easy to create a database instance.

How to create an RDS instance with Terraform

Amazon's [explanation of deleting a versioned object](http://docs.aws.amazon.com/AmazonS3/latest/dev/RemDelMarker.html) and the [SDK documentation](https://docs.aws.amazon.com/sdkforruby/api/Aws/S3/Object.html#delete-instance_method) do not give an example of permanently deleting a versioned object. Here's how to do it.

```ruby
require 'aws-sdk'

s3 = Aws::S3::Resource.new(
  region: 'us-east-1',
  access_key_id: ACCESS_KEY_ID,
  secret_access_key: SECRET_ACCESS_KEY
)
bucket = s3.bucket('my-versioned-bucket')

bucket.objects.each do |object_summary|
  o = bucket.object object_summary.key
  # this is the secret: specify the version while deleting
  o.delete version_id: o.version_id
end
```

If you don't specify the version, you get a delete marker, which you can proceed to delete infinite times and it will not go away :)

Learn how to permanently deleted version objects from AWS S3.

How to permanently delete versioned objects from AWS S3

"How do you do `strftime` in postgres?"

[The answer](https://www.postgresql.org/docs/9.5/static/functions-formatting.html): `to_char(date, format)`.

If you want to group by month, this is what you're looking for:

```
psql=> select count(*), to_char(created_at, 'YYYY-MM') from employees group by to_char(created_at, 'YYYY-MM') order by to_char(created_at,'YYYY-MM') desc;
 count | to_char
-------+---------
    27 | 2016-08
    32 | 2016-07
    58 | 2016-06
    17 | 2016-05
    57 | 2016-04
    44 | 2016-03
    28 | 2016-02
    45 | 2016-01
    10 | 2015-12
    10 | 2015-11
    24 | 2015-10
    15 | 2015-09
    32 | 2015-08
    38 | 2015-07
    31 | 2015-06
    18 | 2015-05
    19 | 2015-04
     5 | 2015-03
     8 | 2015-02
    10 | 2015-01
     7 | 2014-12
    22 | 2014-11
(22 rows)
```

That's it.

How do you do strftime in postgres? Read this straightforward tutorial.

Tech

How to create an RDS instance with Terraform

How to permanently delete versioned objects from AWS S3

How to do Postgres strftime to group by month