What is this IP address: 169.254.169.254?

Solution 1:

These are dynamically configured link-local addresses. They are only valid on a single network segment and are not to be routed.

Of particular note, 169.254.169.254 is used in Amazon EC2 and other cloud computing platforms to distribute metadata to cloud instances.

Solution 2:

In almost all circumstances that's a IP assigned automatically by an interface that's set to get its IP via DHCP but can't get one.

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Solution 3:

It's a IPv4 link local address, as defined in rfc3927. Usually ZeroConfig/Bonjour/mdns et al enabled boxes are setup to have IPv4 ll address to enable (home) networking without the presence of an DHCP or unicast DNS server.

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Solution 4:

This is a special case of an APIPA address. The OP is not asking for 169.254.x.x

As well as being an APIPA address, this is the internal address used by AWS EC2 instances for EC2META queries via HTTP (curl, say).

curl http://169.254.169.254/latest/meta-data/instance-id

will return the instance id without a newline, and this is useful for scripting. It is not used for "distributing" the metadata. Instead, it is used for querying these attributes.