How to connect to remote hashicorp vault server

Question

Let me explain my use-case here,

I wanted to give a try to vault in my local, so I configured VAULT_ADDR as:

$ echo $VAULT_ADDR 
http://127.0.0.1:8200

then I started vault in dev mode (vault server -dev) and everything was ok, I was able to connect to the server.

Then I wrote a really simple config file:

$ cat vault.config 
backend "inmem" {}

listener "tcp" {
  address = "127.0.0.1:8200"
  tls_disable = 1
}

disable_mlock = true

and I restarted the server with vault server -config=vault.config, This too worked fine.

Now I want to use vault server which is deployed in remote server (aws ec2 instance). I have changed content my config file to below

backend "inmem" {}

listener "tcp" {
  address = "123.456.789.1:8200" (aws ec2 public ip)
  tls_disable = 1
}

disable_mlock = true

now this is throwing error

'Error checking seal status: Get "http://123.456.789.1:8200/v1/sys/seal-status": dial tcp 123.456.789.1:8200: connect: connection refused'

when i am trying to check connectivity using telnet command, that too failed.

  telnet 123.456.789.1 8200

'telnet: Unable to connect to remote host: Connection refused'

I have opened 8200 port in security group of aws, and both instances are in same vpc. What I am missing here? Any help?