ec2ssh.sh

ec2ssh.sh

#!/bin/sh

function ec2ssh() {
    sshopt="1246AaCfgKkMNnqsTtVvXxYyb:c:D:e:F:I:i:L:l:m:O:o:p:R:S:W:w:" 

    while getopts $sshopt o ; do done

    hostname=region=""
    if [ $OPTIND -le $# ] ; then
       eval hostarg='$'$OPTIND
       host=${hostarg##*@}  # remove optional user part
       hostname=$(get_ssh_var $host HostName)
       domain=${hostname#ec2*.}
       region=${domain%%.*}
    fi

    if [ -n "$host" -a -n "hostname" -a -n "$region" ] ; then
       echo "refreshing hostname from EC2.."
       new_hostname=$(ec2-public-dns $host $region)
       if [ $hostname != $new_hostname ] ; then
           echo "hostname changed to $new_hostname"
           replace_ssh_val $host $hostname $new_hostname
       fi
    fi

    /usr/bin/ssh "$@"
    return $?
}

get_public_dns.py

#!/usr/bin/env python
import botocore.session


def get_public_dns_name(host, region):
    session = botocore.session.get_session()
    ec2 = session.get_service('ec2')
    r, d = ec2.get_operation('DescribeInstances').call(
        ec2.get_endpoint(region_name=region),
        filters=[{'Name': 'tag:Name', 'Values': [host]}])
    r.raise_for_status()
    return d['Reservations'][0]['Instances'][0]['PublicDnsName']


if __name__ == "__main__":
    import sys
    host = sys.argv[1]
    region = sys.argv[2]
    print get_public_dns_name(host, region)

ssh-cfg-util.sh

# sed routines to manage hostnames ssh config 

_ssh_cfg="$HOME/.ssh/config"

# sed loop over host stanzas in ssh config
_s_pre=':s
n
/^$/{
n
t
}'

_s_post='t
b s'

get_ssh_var() {
    cat $_ssh_cfg | sed -n "/Host $1/{$_s_pre
s/$2 //p;$_s_post
}"
}

replace_ssh_val(){ 
    # usage: replace_ssh_val host old new [varname]
    sed -i orig "/Host $1/{$_s_pre
s/$4 $2/$4 $3/;$_s_post
}" $_ssh_cfg
}