instance_events: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/instance_events - from package: python2-boto
/usr/bin/instance_events - from package: python-boto

You may install the required package with command yum install {package}

Error in other languages:
instance_events: bevel nie gevind nie
instance_events: comandă negăsită
instance_events: comando não encontrado
instance_events: commande introuvable
instance_events: command not found
instance_events: käsku ei ole
instance_events: không tìm thấy lệnh
instance_events: komanda nerasta
instance_events: Kommando nicht gefunden.
instance_events: kommandot finns inte
instance_events: komut yok
instance_events: nie znaleziono polecenia
instance_events: níor aimsíodh an t-ordú
instance_events: no se encontró la orden
instance_events: no s'ha trobat l'ordre
instance_events: opdracht niet gevonden
instance_events: parancs nem található
instance_events: perintah tidak ditemukan
instance_events: príkaz nenájdený
instance_events: příkaz nenalezen
instance_events: команда не найдена
instance_events: командата не е открита
instance_events: 命令找不到
instance_events: コマンドが見つかりません