[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

(The more valuable and massive a data set is, the less likely it's in a format you can just parse. Has anybody else noticed that?)

Here's how to convert a fixed-width file to CSV with the [standard GNU unix tool `gawk`](https://www.gnu.org/software/gawk/):

### Theoretical (i.e., see "real life" below)

Thanks to [stackoverflow](http://stackoverflow.com/questions/28561786/convert-a-fixed-width-file-from-text-to-csv): (reproducing verbatim)

```
gawk '$1=$1' OFS=, FIELDWIDTHS='4 2 5 1 1' infile > outfile.csv
```

Where `FIELDWIDTHS` is a list of field widths and `OFS` is the output file separator.

### Real life

In real life, fixed width files contain commas and double quotes.

```
# put this in a file called fixed2csv.awk
{
  for (i=1;i<=NF;i++) {
    sub(/\s+$/,"",$i)
    sub("\"","\"\"",$i)
    printf "\"%s\"%s", $i, (i<NF?OFS:ORS)
  }
}
```

Then run it on your data:

```
gawk -f fixed2csv.awk OFS=, FIELDWIDTHS='4 2 5 1 1' infile > outfile.csv
```

Thanks to [Ed Morton on Stackoverflow](http://stackoverflow.com/questions/31947383/fixed-width-to-csv) for inspiration!

Learn how to convert a fixed-width file to CSV with the standard GNU unix tool gawk

How to convert a fixed-width file into CSV

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.

All posts

How to create an RDS instance with Terraform

How to convert a fixed-width file into CSV

How to permanently delete versioned objects from AWS S3

How to do Postgres strftime to group by month