User-Data Formats¶
User data that will be acted upon by cloud-init must be in one of the following types.
Gzip Compressed Content¶
Content found to be gzip compressed will be uncompressed. The uncompressed data will then be used as if it were not compressed. This is typically useful because user-data is limited to ~16384 [1] bytes.
Mime Multi Part Archive¶
This list of rules is applied to each part of this multi-part file. Using a mime-multi part file, the user can specify more than one type of data.
For example, both a user data script and a cloud-config type could be specified.
Supported content-types are listed from the cloud-init subcommand make-mime:
$ cloud-init devel make-mime --list-types
cloud-boothook
cloud-config
cloud-config-archive
cloud-config-jsonp
jinja2
part-handler
upstart-job
x-include-once-url
x-include-url
x-shellscript
Helper subcommand to generate mime messages¶
The cloud-init subcommand can generate MIME multi-part files: make-mime.
make-mime
subcommand takes pairs of (filename, “text/” mime subtype)
separated by a colon (e.g. config.yaml:cloud-config
) and emits a MIME
multipart message to stdout. An example invocation, assuming you have your
cloud config in config.yaml
and a shell script in script.sh
and want
to store the multipart message in user-data
:
$ cloud-init devel make-mime -a config.yaml:cloud-config -a script.sh:x-shellscript > user-data
User-Data Script¶
Typically used by those who just want to execute a shell script.
Begins with: #!
or Content-Type: text/x-shellscript
when using a MIME
archive.
Note
New in cloud-init v. 18.4: User-data scripts can also render cloud instance metadata variables using jinja templating. See Instance Metadata for more information.
Example¶
$ cat myscript.sh
#!/bin/sh
echo "Hello World. The time is now $(date -R)!" | tee /root/output.txt
$ euca-run-instances --key mykey --user-data-file myscript.sh ami-a07d95c9
Include File¶
This content is a include
file.
The file contains a list of urls, one per line. Each of the URLs will be read, and their content will be passed through this same set of rules. Ie, the content read from the URL can be gzipped, mime-multi-part, or plain text. If an error occurs reading a file the remaining files will not be read.
Begins with: #include
or Content-Type: text/x-include-url
when using
a MIME archive.
Cloud Config Data¶
Cloud-config is the simplest way to accomplish some things via user-data. Using cloud-config syntax, the user can specify certain things in a human friendly format.
These things include:
- apt upgrade should be run on first boot
- a different apt mirror should be used
- additional apt sources should be added
- certain SSH keys should be imported
- and many more…
Note
This file must be valid yaml syntax.
See the Cloud config examples section for a commented set of examples of supported cloud config formats.
Begins with: #cloud-config
or Content-Type: text/cloud-config
when
using a MIME archive.
Note
New in cloud-init v. 18.4: Cloud config data can also render cloud instance metadata variables using jinja templating. See Instance Metadata for more information.
Upstart Job¶
Content is placed into a file in /etc/init
, and will be consumed by upstart
as any other upstart job.
Begins with: #upstart-job
or Content-Type: text/upstart-job
when using
a MIME archive.
Cloud Boothook¶
This content is boothook
data. It is stored in a file under
/var/lib/cloud
and then executed immediately. This is the earliest hook
available. Note, that there is no mechanism provided for running only once. The
boothook must take care of this itself.
It is provided with the instance id in the environment variable
INSTANCE_ID
. This could be made use of to provide a ‘once-per-instance’
type of functionality.
Begins with: #cloud-boothook
or Content-Type: text/cloud-boothook
when
using a MIME archive.
Part Handler¶
This is a part-handler
: It contains custom code for either supporting new
mime-types in multi-part user data, or overriding the existing handlers for
supported mime-types. It will be written to a file in /var/lib/cloud/data
based on its filename (which is generated).
This must be python code that contains a list_types
function and a
handle_part
function. Once the section is read the list_types
method
will be called. It must return a list of mime-types that this part-handler
handles. Because mime parts are processed in order, a part-handler
part
must precede any parts with mime-types it is expected to handle in the same
user data.
The handle_part
function must be defined like:
def handle_part(data, ctype, filename, payload):
# data = the cloudinit object
# ctype = "__begin__", "__end__", or the mime-type of the part that is being handled.
# filename = the filename of the part (or a generated filename if none is present in mime data)
# payload = the parts' content
Cloud-init will then call the handle_part
function once before it handles
any parts, once per part received, and once after all parts have been handled.
The '__begin__'
and '__end__'
sentinels allow the part handler to do
initialization or teardown before or after receiving any parts.
Begins with: #part-handler
or Content-Type: text/part-handler
when
using a MIME archive.
Example¶
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | #part-handler
def list_types():
# return a list of mime-types that are handled by this module
return(["text/plain", "text/go-cubs-go"])
def handle_part(data,ctype,filename,payload):
# data: the cloudinit object
# ctype: '__begin__', '__end__', or the specific mime-type of the part
# filename: the filename for the part, or dynamically generated part if
# no filename is given attribute is present
# payload: the content of the part (empty for begin or end)
if ctype == "__begin__":
print "my handler is beginning"
return
if ctype == "__end__":
print "my handler is ending"
return
print "==== received ctype=%s filename=%s ====" % (ctype,filename)
print payload
print "==== end ctype=%s filename=%s" % (ctype, filename)
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Also this blog post offers another example for more advanced usage.
Kernel Command Line¶
When using the NoCloud datasource, users can pass user data via the kernel command line parameters. See the NoCloud datasource documentation for more details.
Disabling User-Data¶
Cloud-init can be configured to ignore any user-data provided to instance.
This allows custom images to prevent users from accidentally breaking closed
appliances. Setting allow_userdata: false
in the configuration will disable
cloud-init from processing user-data.
[1] | See your cloud provider for applicable user-data size limitations… |