This morning i was alerted to the fact that both apache instances serving my app were not responding to requests from my load balancer. I attempted apachectl restart and it said apache was not running. So, i started apache on both instances and got the service up again. I then followed the logs and worked out that both had performed upgrades via the unattended-upgrades package moments before they stopped responding.

/var/log/unattended-upgrades/unattended-upgrades.log

2013-07-02 06:30:51,875 INFO Starting unattended upgrades script
2013-07-02 06:30:51,875 INFO Allowed origins are: ['o=Ubuntu,a=precise-security']
2013-07-02 06:33:57,771 INFO Packages that are upgraded: accountsservice apache2 apache2-mpm-prefork apache2-utils apache2.2-bin apache2.2-common apparmor apport apt apt-transport-https apt-utils bind9-host binutils dbus dnsutils gnupg gpgv isc-dhcp-client isc-dhcp-common krb5-locales libaccountsservice0 libapt-inst1.4 libapt-pkg4.12 libbind9-80 libc-bin libc-dev-bin libc6 libc6-dev libcurl3-gnutls libdbus-1-3 libdbus-glib-1-2 libdns81 libdrm-intel1 libdrm-nouveau1a libdrm-radeon1 libdrm2 libexpat1 libfreetype6 libgc1c2 libgnutls-dev libgnutls-openssl27 libgnutls26 libgnutlsxx27 libisc83 libisccc80 libisccfg82 liblwres80 libruby1.8 libx11-6 libx11-data libxcb1 libxext6 libxml2 linux-firmware linux-image-virtual linux-libc-dev linux-virtual multiarch-support openssl perl perl-base perl-modules python-apport python-crypto python-keyring python-problem-report python-software-properties ri1.8 ruby1.8 ruby1.8-dev sudo tzdata update-manager-core
2013-07-02 06:33:57,772 INFO Writing dpkg log to '/var/log/unattended-upgrades/unattended-upgrades-dpkg_2013-07-02_06:33:57.772399.log'
2013-07-02 06:36:10,584 INFO All upgrades installed

I'm running Ubuntu 12.04 on Amazon EC2 servers. I have unattended-upgrades installed and configured as follows:

/etc/apt/apt.conf.d/50unattended-upgrades

// Automatically upgrade packages from these (origin:archive) pairs
Unattended-Upgrade::Allowed-Origins {
    "${distro_id}:${distro_codename}-security";
//  "${distro_id}:${distro_codename}-updates";
//  "${distro_id}:${distro_codename}-proposed";
//  "${distro_id}:${distro_codename}-backports";
};

// List of packages to not update
Unattended-Upgrade::Package-Blacklist {
};

/etc/apt/apt.conf.d/20auto-upgrades

APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Unattended-Upgrade "1";

I've struggled to find documentation about what happens to running processes during an upgrade.

- Is this expected behaviour? Or should unattended-upgrades restart apache after upgrading it? - What can I do to ensure apache is restarted correctly? Should I just blacklist the apache package?