Sometimes you want to retrieve EC2 insntances' region information.

You can query that information through instance metadata(169.254.169.254).
```
$ curl --silent http://169.254.169.254/latest/dynamic/instance-identity/document
{
  "privateIp" : "172.31.2.15",
  "instanceId" : "i-12341ee8",
  "billingProducts" : null,
  "instanceType" : "t2.small",
  "accountId" : "1234567890",
  "pendingTime" : "2015-11-03T03:09:54Z",
  "imageId" : "ami-383c1956",
  "kernelId" : null,
  "ramdiskId" : null,
  "architecture" : "x86_64",
  "region" : "ap-northeast-1", # <- region
  "version" : "2010-08-31",
  "availabilityZone" : "ap-northeast-1c",
  "devpayProductCodes" : null
}
```
Response's JSON has a `region` key, so if you just want to get region, filter the key with `jq`.

```
$ sudo yum install -y jq
$ curl --silent http://169.254.169.254/latest/dynamic/instance-identity/document | jq -r .region
ap-northeast-1
```
## Usecase : set aws-cli's region

Even if you launch an EC2 instance with IAM role, you can't run commands without supplying region info. Otherwise, you'll encounter errors as follows. 
```
$ aws ec2 describe-vpcs
You must specify a region. You can also configure your region by running "aws configure".
```

Here's how to set aws-cli's region.

First, check the curren settings.

```
$ aws configure  list
      Name                    Value             Type    Location
      ----                    -----             ----    --------
   profile                <not set>             None    None
access_key     ****************GVKA         iam-role
secret_key     ****************bll+         iam-role
    region                <not set>             None    None
```
`region` is not set.

Now pass metadata's region to `aws configure set region` command.

```
$ aws configure set region `curl --silent http://169.254.169.254/latest/dynamic/instance-identity/document | jq -r .region`
$ aws configure get region
ap-northeast-1
$ aws configure list
      Name                    Value             Type    Location
      ----                    -----             ----    --------
   profile                <not set>             None    None
access_key     ****************GVKA         iam-role
secret_key     ****************bll+         iam-role
    region           ap-northeast-1      config-file    ~/.aws/config
$ cat ~/.aws/config
[default]
region = ap-northeast-1
```

### UserData
To configure API region, just add following code to you UserData.

```
#!/bin/bash
yum install -y jq
REGION=`curl -s http://169.254.169.254/latest/dynamic/instance-identity/document | jq .region -r`
sudo -u ec2-user aws configure set region $REGION
```