The EC2 datasource is the oldest and most widely used datasource that
cloud-init supports. This datasource interacts with a magic ip that is
provided to the instance by the cloud provider. Typically this ip is
169.254.169.254 of which at this ip a http server is provided to the
instance so that the instance can make calls to get instance userdata and
Metadata is accessible via the following URL:
GET http://169.254.169.254/2009-04-04/meta-data/ ami-id ami-launch-index ami-manifest-path block-device-mapping/ hostname instance-id instance-type local-hostname local-ipv4 placement/ public-hostname public-ipv4 public-keys/ reservation-id security-groups
Userdata is accessible via the following URL:
GET http://169.254.169.254/2009-04-04/user-data 1234,fred,reboot,true | 4512,jimbo, | 173,,,
Note that there are multiple versions of this data provided, cloud-init by default uses 2009-04-04 but newer versions can be supported with relative ease (newer versions have more data exposed, while maintaining backward compatibility with the previous versions). Version 2016-09-02 is required for secondary IP address support.
To see which versions are supported from your cloud provider use the following URL:
GET http://169.254.169.254/ 1.0 2007-01-19 2007-03-01 2007-08-29 2007-10-10 2007-12-15 2008-02-01 2008-09-01 2009-04-04 ... latest
The following configuration can be set for the datasource in system configuration (in /etc/cloud/cloud.cfg or /etc/cloud/cloud.cfg.d/).
The settings that may be configured are:
- metadata_urls: This list of urls will be searched for an Ec2 metadata service. The first entry that successfully returns a 200 response for <url>/<version>/meta-data/instance-id will be selected. (default: [’http://169.254.169.254’, ‘http://instance-data:8773’]).
- max_wait: the maximum amount of clock time in seconds that should be spent searching metadata_urls. A value less than zero will result in only one request being made, to the first in the list. (default: 120)
- timeout: the timeout value provided to urlopen for each individual http request. This is used both when selecting a metadata_url and when crawling the metadata service. (default: 50)
- apply_full_imds_network_config: Boolean (default: True) to allow cloud-init to configure any secondary NICs and secondary IPs described by the metadata service. All network interfaces are configured with DHCP (v4) to obtain an primary IPv4 address and route. Interfaces which have a non-empty ‘ipv6s’ list will also enable DHCPv6 to obtain a primary IPv6 address and route. The DHCP response (v4 and v6) return an IP that matches the first element of local-ipv4s and ipv6s lists respectively. All additional values (secondary addresses) in the static ip lists will be added to interface.
An example configuration with the default values is provided below:
datasource: Ec2: metadata_urls: ["http://169.254.169.254:80", "http://instance-data:8773"] max_wait: 120 timeout: 50 apply_full_imds_network_config: true
- There are 2 types of EC2 instances network-wise: VPC ones (Virtual Private Cloud) and Classic ones (also known as non-VPC). One major difference between them is that Classic instances have their MAC address changed on stop/restart operations, so cloud-init will recreate the network config file for EC2 Classic instances every boot. On VPC instances this file is generated only in the first boot of the instance. The check for the instance type is performed by is_classic_instance() method.
- For EC2 instances with multiple network interfaces (NICs) attached, dhcp4 will be enabled to obtain the primary private IPv4 address of those NICs. Wherever dhcp4 or dhcp6 is enabled for a NIC, a dhcp route-metric will be added with the value of
<device-number + 1> * 100to ensure dhcp routes on the primary NIC are preferred to any secondary NICs. For example: the primary NIC will have a DHCP route-metric of 100, the next NIC will be 200.