IP Address Assigned to EC2 Instance

1. When an EC2 instance is started, what actually provides the IP addresses that are assigned to it?

According to the document, a public IP address is assigned to your instance from Amazon's pool of public IPv4 addresses.

A public IP address is assigned to your instance from Amazon's pool of public IPv4 addresses, and is not associated with your AWS account. When a public IP address is disassociated from your instance, it is released back into the public IPv4 address pool, and you cannot reuse it.

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-instance-addressing.html#concepts-public-addresses

2. How can I see the public IP address assigned to an EC2 instance, from within (i.e. after connecting) the EC2 instance?

Instance metadata can be used to retrieve public IP addresses.

curl http://169.254.169.254/latest/meta-data/public-ipv4

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instancedata-data-retrieval.html

I got the private ip address with the help of this post in my Ubuntu instance.

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc mq state UP group default qlen 1000
    link/ether 02:93:07:be:da:d9 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.76/24 brd 10.0.0.255 scope global dynamic eth0
       valid_lft 2915sec preferred_lft 2915sec
    inet6 fe80::93:7ff:febe:dad9/64 scope link 
       valid_lft forever preferred_lft forever

It is same with the ip address in the following command.

TOKEN=`curl -X PUT "http://169.254.169.254/latest/api/token" -H "X-aws-ec2-metadata-token-ttl-seconds: 21600"` && curl -H "X-aws-ec2-metadata-token: $TOKEN" -v http://169.254.169.254/latest/meta-data/local-ipv4
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    56  100    56    0     0  28000      0 --:--:-- --:--:-- --:--:-- 28000
*   Trying 169.254.169.254:80...
* TCP_NODELAY set
* Connected to 169.254.169.254 (169.254.169.254) port 80 (#0)
> GET /latest/meta-data/local-ipv4 HTTP/1.1
> Host: 169.254.169.254
> User-Agent: curl/7.68.0
> Accept: */*
> X-aws-ec2-metadata-token: AQAAAEKVNCUakqrrHX0SIzCtzRcmpmaNNl2ypoguN1KR6NpvRlCnoQ==
> 
* Mark bundle as not supporting multiuse
* HTTP 1.0, assume close after body
< HTTP/1.0 200 OK
< Accept-Ranges: bytes
< Content-Length: 9
< Content-Type: text/plain
< Date: Tue, 29 Nov 2022 11:37:08 GMT
< Last-Modified: Wed, 23 Nov 2022 18:36:36 GMT
< X-Aws-Ec2-Metadata-Token-Ttl-Seconds: 21600
< Connection: close
< Server: EC2ws
< 
* Closing connection 0
10.0.0.76

But I can not get the public ip address with the curl command.

curl http://169.254.169.254/latest/meta-data/public-ipv4

Looks like there is no public-ipv4 under meta-data directory.

$ TOKEN=`curl -X PUT "http://169.254.169.254/latest/api/token" -H "X-aws-ec2-metadata-token-ttl-seconds: 21600"` && curl -H "X-aws-ec2-metadata-token: $TOKEN" -v http://169.254.169.254/latest/meta-data
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100    56  100    56    0     0  28000      0 --:--:-- --:--:-- --:--:-- 56000
*   Trying 169.254.169.254:80...
* TCP_NODELAY set
* Connected to 169.254.169.254 (169.254.169.254) port 80 (#0)
> GET /latest/meta-data HTTP/1.1
> Host: 169.254.169.254
> User-Agent: curl/7.68.0
> Accept: */*
> X-aws-ec2-metadata-token: AQAAAEKVNCUB3KPoodSB0SFUkkn1aSah2MRUxAVQQx_3SeVBllVoFA==
> 
* Mark bundle as not supporting multiuse
* HTTP 1.0, assume close after body
< HTTP/1.0 200 OK
< Accept-Ranges: bytes
< Content-Length: 324
< Content-Type: text/plain
< Date: Tue, 29 Nov 2022 11:29:43 GMT
< Last-Modified: Wed, 23 Nov 2022 18:36:36 GMT
< X-Aws-Ec2-Metadata-Token-Ttl-Seconds: 21600
< Connection: close
< Server: EC2ws
< 
ami-id
ami-launch-index
ami-manifest-path
auth-identity-credentials/
block-device-mapping/
events/
hostname
iam/
identity-credentials/
instance-action
instance-id
instance-life-cycle
instance-type
local-hostname
local-ipv4
mac
metrics/
network/
placement/
profile
public-keys/
reservation-id
security-groups
services/