Facebook and Instagram services suffered another outage on Friday 8 October, following a huge crash earlier that week.
WhatsApp and Facebook Messenger also experienced intermittent issues. The cause of the outage was not disclosed.
"We’re aware that some people are having trouble accessing our apps and products," Facebook said during the outage. "We’re working to get things back to normal as quickly as possible and we apologize for any inconvenience."
The outage lasted over an hour, and wider issues persisted for another hour or two.
That's an improvement on Facebook's Monday outage, which lasted nearly seven hours.
That time, a command was issued with the intention to assess the availability of global backbone capacity during routine maintenance of Facebook's global backbone network "which unintentionally took down all the connections in our backbone network, effectively disconnecting Facebook data centers globally," the company's VP of infrastructure Santosh Janardhan said in a blog post.
"Our systems are designed to audit commands like these to prevent mistakes like this, but a bug in that audit tool prevented it from properly stopping the command."
The command caused a complete disconnection of Facebook's server connections between its data centers and the Internet. "And that total loss of connection caused a second issue that made things worse," Janardhan said.
He explained: "One of the jobs performed by our smaller facilities is to respond to DNS queries. DNS is the address book of the internet, enabling the simple web names we type into browsers to be translated into specific server IP addresses. Those translation queries are answered by our authoritative name servers that occupy well known IP addresses themselves, which in turn are advertised to the rest of the Internet via another protocol called the border gateway protocol (BGP)."
Facebook's DNS servers disable BGP advertisements if they themselves can not speak to the data centers, since this is an indication of an unhealthy network connection. With this outage, the entire backbone appeared unhealthy causing the BGP advertisements to be withdrawn.
"The end result was that our DNS servers became unreachable even though they were still operational," Janardhan said. "This made it impossible for the rest of the Internet to find our servers."