There are a variety of options to configure the software which runs on the servers in your stack. These can be broadly divided into the following:
This section will describe each of these options and provide examples for using them together in your stacks.
The first opportunity to influence what software is configured on your servers is by booting them with a custom-built image. There are a number of reasons you might want to do this, including:
A number of tools are available for building custom images, including:
Examples in this guide which require custom images will use diskimage-builder.
When booting a server it is possible to specify the contents of the user-data to be passed to that server. This user-data is made available either from configured config-drive or from the Metadata service.
How this user-data is consumed depends on the image being booted, but the most commonly used tool for default cloud images is Cloud-init.
Whether the image is using Cloud-init or not, it should be possible to specify a shell script in the user_data property and have it be executed by the server during boot:
1 2 3 4 5 6 7 8 9 10 | resources:
the_server:
type: OS::Nova::Server
properties:
# flavor, image etc
user_data: |
#!/bin/bash
echo "Running boot script"
# ...
|
Note
Debugging these scripts it is often useful to view the boot log using nova console-log <server-id> to view the progress of boot script execution.
Often there is a need to set variable values based on parameters or resources in the stack. This can be done with the str_replace intrinsic function:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | parameters:
foo:
default: bar
resources:
the_server:
type: OS::Nova::Server
properties:
# flavor, image etc
user_data:
str_replace:
template: |
#!/bin/bash
echo "Running boot script with $FOO"
# ...
params:
$FOO: {get_param: foo}
|
Warning
If a stack-update is performed and there are any changes at all to the content of user_data then the server will be replaced (deleted and recreated) so that the modified boot configuration can be run on a new server.
When these scripts grow it can become difficult to maintain them inside the template, so the get_file intrinsic function can be used to maintain the script in a separate file:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | parameters:
foo:
default: bar
resources:
the_server:
type: OS::Nova::Server
properties:
# flavor, image etc
user_data:
str_replace:
template: {get_file: the_server_boot.sh}
params:
$FOO: {get_param: foo}
|
Note
str_replace can replace any strings, not just strings starting with $. However doing this for the above example is useful because the script file can be executed for testing by passing in environment variables.
The OS::Nova::Server user_data_format property determines how the user_data should be formatted for the server. For the default value HEAT_CFNTOOLS, the user_data is bundled as part of the heat-cfntools cloud-init boot configuration data. While HEAT_CFNTOOLS is the default for user_data_format, it is considered legacy and RAW or SOFTWARE_CONFIG will generally be more appropriate.
For RAW the user_data is passed to Nova unmodified. For a Cloud-init enabled image, the following are both valid RAW user-data:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | resources:
server_with_boot_script:
type: OS::Nova::Server
properties:
# flavor, image etc
user_data_format: RAW
user_data: |
#!/bin/bash
echo "Running boot script"
# ...
server_with_cloud_config:
type: OS::Nova::Server
properties:
# flavor, image etc
user_data_format: RAW
user_data: |
#cloud-config
final_message: "The system is finally up, after $UPTIME seconds"
|
For SOFTWARE_CONFIG user_data is bundled as part of the software config data, and metadata is derived from any associated Software deployment resources.
Often it is necessary to pause further creation of stack resources until the boot configuration script has notified that it has reached a certain state. This is usually either to notify that a service is now active, or to pass out some generated data which is needed by another resource. The resources OS::Heat::WaitCondition and OS::Heat::SwiftSignal both perform this function using different techniques and tradeoffs.
OS::Heat::WaitCondition is implemented as a call to the Orchestration API resource signal. The token is created using credentials for a user account which is scoped only to the wait condition handle resource. This user is created when the handle is created, and is associated to a project which belongs to the stack, in an identity domain which is dedicated to the orchestration service.
Sending the signal is a simple HTTP request, as with this example using curl:
curl -i -X POST -H 'X-Auth-Token: <token>' \
-H 'Content-Type: application/json' -H 'Accept: application/json' \
'<wait condition URL>' --data-binary '<json containing signal data>'
The JSON containing the signal data is expected to be of the following format:
{
"status": "SUCCESS",
"reason": "The reason which will appear in the 'heat event-list' output",
"data": "Data to be used elsewhere in the template via get_attr",
"id": "Optional unique ID of signal"
}
All of these values are optional, and if not specified will be set to the following defaults:
{
"status": "SUCCESS",
"reason": "Signal <id> received",
"data": null,
"id": "<sequential number starting from 1 for each signal received>"
}
If status is set to FAILURE then the resource (and the stack) will go into a FAILED state using the reason as failure reason.
The following template example uses the convenience attribute curl_cli which builds a curl command with a valid token:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 | resources:
wait_condition:
type: OS::Heat::WaitCondition
properties:
handle: {get_resource: wait_handle}
# Note, count of 5 vs 6 is due to duplicate signal ID 5 sent below
count: 5
timeout: 300
wait_handle:
type: OS::Heat::WaitConditionHandle
the_server:
type: OS::Nova::Server
properties:
# flavor, image etc
user_data_format: RAW
user_data:
str_replace:
template: |
#!/bin/sh
# Below are some examples of the various ways signals
# can be sent to the Handle resource
# Simple success signal
wc_notify --data-binary '{"status": "SUCCESS"}'
# Or you optionally can specify any of the additional fields
wc_notify --data-binary '{"status": "SUCCESS", "reason": "signal2"}'
wc_notify --data-binary '{"status": "SUCCESS", "reason": "signal3", "data": "data3"}'
wc_notify --data-binary '{"status": "SUCCESS", "reason": "signal4", "id": "id4", "data": "data4"}'
# If you require control of the ID, you can pass it.
# The ID should be unique, unless you intend for duplicate
# signals to overwrite each other. The following two calls
# do the exact same thing, and will be treated as one signal
# (You can prove this by changing count above to 7)
wc_notify --data-binary '{"status": "SUCCESS", "id": "id5"}'
wc_notify --data-binary '{"status": "SUCCESS", "id": "id5"}'
# Example of sending a failure signal, optionally
# reason, id, and data can be specified as above
# wc_notify --data-binary '{"status": "FAILURE"}'
params:
wc_notify: { get_attr: [wait_handle, curl_cli] }
outputs:
wc_data:
value: { get_attr: [wait_condition, data] }
# this would return the following json
# {"1": null, "2": null, "3": "data3", "id4": "data4", "id5": null}
wc_data_4:
value: { 'Fn::Select': ['id4', { get_attr: [wait_condition, data] }] }
# this would return "data4"
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OS::Heat::SwiftSignal is implemented by creating an Object Storage API temporary URL which is populated with signal data with an HTTP PUT. The orchestration service will poll this object until the signal data is available. Object versioning is used to store multiple signals.
Sending the signal is a simple HTTP request, as with this example using curl:
curl -i -X PUT '<object URL>' --data-binary '<json containing signal data>'
The above template example only needs to have the type changed to the swift signal resources:
1 2 3 4 5 6 7 8 9 10 | resources:
signal:
type: OS::Heat::SwiftSignal
properties:
handle: {get_resource: wait_handle}
timeout: 300
signal_handle:
type: OS::Heat::SwiftSignalHandle
# ...
|
The decision to use OS::Heat::WaitCondition or OS::Heat::SwiftSignal will depend on a few factors:
Boot configuration scripts can also be managed as their own resources. This allows configuration to be defined once and run on multiple server resources. These software-config resources are stored and retrieved via dedicated calls to the Orchestration API. It is not possible to modify the contents of an existing software-config resource, so a stack-update which changes any existing software-config resource will result in API calls to create a new config and delete the old one.
The resource OS::Heat::SoftwareConfig is used for storing configs represented by text scripts, for example:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | resources:
boot_script:
type: OS::Heat::SoftwareConfig
properties:
group: ungrouped
config: |
#!/bin/bash
echo "Running boot script"
# ...
server_with_boot_script:
type: OS::Nova::Server
properties:
# flavor, image etc
user_data_format: RAW
user_data: {get_resource: boot_script}
|
The resource OS::Heat::CloudConfig allows Cloud-init cloud-config to be represented as template YAML rather than a block string. This allows intrinsic functions to be included when building the cloud-config. This also ensures that the cloud-config is valid YAML, although no further checks for valid cloud-config are done.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | parameters:
file_content:
type: string
description: The contents of the file /tmp/file
resources:
boot_config:
type: OS::Heat::CloudConfig
properties:
cloud_config:
write_files:
- path: /tmp/file
content: {get_param: file_content}
server_with_cloud_config:
type: OS::Nova::Server
properties:
# flavor, image etc
user_data_format: RAW
user_data: {get_resource: boot_config}
|
The resource OS::Heat::MultipartMime allows multiple OS::Heat::SoftwareConfig and OS::Heat::CloudConfig resources to be combined into a single Cloud-init multi-part message:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 | parameters:
file_content:
type: string
description: The contents of the file /tmp/file
other_config:
type: string
description: The ID of a software-config resource created elsewhere
resources:
boot_config:
type: OS::Heat::CloudConfig
properties:
cloud_config:
write_files:
- path: /tmp/file
content: {get_param: file_content}
boot_script:
type: OS::Heat::SoftwareConfig
properties:
group: ungrouped
config: |
#!/bin/bash
echo "Running boot script"
# ...
server_init:
type: OS::Heat::MultipartMime
properties:
parts:
- config: {get_resource: boot_config}
- config: {get_resource: boot_script}
- config: {get_param: other_config}
server:
type: OS::Nova::Server
properties:
# flavor, image etc
user_data_format: RAW
user_data: {get_resource: server_init}
|
There are many situations where it is not desirable to replace the server whenever there is a configuration change. The OS::Heat::SoftwareDeployment resource allows any number of software configurations to be added or removed from a server throughout its life-cycle.
OS::Heat::SoftwareConfig resources are used to store software configuration, and a OS::Heat::SoftwareDeployment resource is used to associate a config resource with one server. The group attribute on OS::Heat::SoftwareConfig specifies what tool will consume the config content.
OS::Heat::SoftwareConfig has the ability to define a schema of inputs and which the configuration script supports. Inputs are mapped to whatever concept the configuration tool has for assigning variables/parameters.
Likewise, outputs are mapped to the tool’s capability to export structured data after configuration execution. For tools which do not support this, outputs can always be written to a known file path for the hook to read.
The OS::Heat::SoftwareDeployment resource allows values to be assigned to the config inputs, and the resource remains in an IN_PROGRESS state until the server signals to heat what (if any) output values were generated by the config script.
Each of the following examples requires that the servers be booted with a custom image. The following script uses diskimage-builder to create an image required in later examples:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 | # Clone the required repositories. Some of these are also available
# via pypi or as distro packages.
git clone https://git.openstack.org/openstack/diskimage-builder.git
git clone https://git.openstack.org/openstack/tripleo-image-elements.git
git clone https://git.openstack.org/openstack/heat-templates.git
# Required by diskimage-builder to discover element collections
export ELEMENTS_PATH=tripleo-image-elements/elements:heat-templates/hot/software-config/elements
# The base operating system element(s) provided by the diskimage-builder
# elements collection. Other values which may work include:
# centos7, debian, opensuse, rhel, rhel7, or ubuntu
export BASE_ELEMENTS="fedora selinux-permissive"
# Install and configure the os-collect-config agent to poll the heat service
# for configuration changes to execute
export AGENT_ELEMENTS="os-collect-config os-refresh-config os-apply-config"
# heat-config installs an os-refresh-config script which will invoke the
# appropriate hook to perform configuration. The element heat-config-script
# installs a hook to perform configuration with shell scripts
export DEPLOYMENT_BASE_ELEMENTS="heat-config heat-config-script"
# Install a hook for any other chosen configuration tool(s).
# Elements which install hooks include:
# heat-config-cfn-init, heat-config-puppet, or heat-config-salt
export DEPLOYMENT_TOOL=""
# The name of the qcow2 image to create, and the name of the image
# uploaded to the OpenStack image registry.
export IMAGE_NAME=fedora-software-config
# Create the image
diskimage-builder/bin/disk-image-create vm $BASE_ELEMENTS $AGENT_ELEMENTS \
$DEPLOYMENT_BASE_ELEMENTS $DEPLOYMENT_TOOL -o $IMAGE_NAME.qcow2
# Upload the image, assuming valid credentials are already sourced
glance image-create --disk-format qcow2 --container-format bare \
--name $IMAGE_NAME < $IMAGE_NAME.qcow2
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The Custom image script already includes the heat-config-script element so the built image will already have the ability to configure using shell scripts.
Config inputs are mapped to shell environment variables. The script can communicate outputs to heat by writing to the $heat_outputs_path.output name file. See the following example for a script which expects inputs foo, bar and generates an output result.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 | resources:
config:
type: OS::Heat::SoftwareConfig
properties:
group: script
inputs:
- name: foo
- name: bar
outputs:
- name: result
config: |
#!/bin/sh -x
echo "Writing to /tmp/$bar"
echo $foo > /tmp/$bar
echo -n "The file /tmp/$bar contains `cat /tmp/$bar` for server $deploy_server_id during $deploy_action" > $heat_outputs_path.result
echo "Written to /tmp/$bar"
echo "Output to stderr" 1>&2
deployment:
type: OS::Heat::SoftwareDeployment
properties:
config:
get_resource: config
server:
get_resource: server
input_values:
foo: fooooo
bar: baaaaa
server:
type: OS::Nova::Server
properties:
# flavor, image etc
user_data_format: SOFTWARE_CONFIG
outputs:
result:
value:
get_attr: [deployment, result]
stdout:
value:
get_attr: [deployment, deploy_stdout]
stderr:
value:
get_attr: [deployment, deploy_stderr]
status_code:
value:
get_attr: [deployment, deploy_status_code]
|
Note
A config resource can be associated with multiple deployment resources, and each deployment can specify the same or different values for the server and input_values properties.
As can be seen in the outputs section of the above template, the result config output value is available as an attribute on the deployment resource. Likewise the captured stdout, stderr and status_code are also available as attributes.
The agent toolchain of os-collect-config, os-refresh-config and os-apply-config can actually be used on their own to inject heat stack configuration data into a server running a custom image.
The custom image needs to have the following to use this approach:
The projects tripleo-image-elements and tripleo-heat-templates demonstrate this approach.
Likely the only reason to use the cfn-init hook is to migrate templates which contain AWS::CloudFormation::Init metadata without needing a complete rewrite of the config metadata. It is included here as it introduces a number of new concepts.
To use the cfn-init tool the heat-config-cfn-init element is required to be on the built image, so Custom image script needs to be modified with the following:
export DEPLOYMENT_TOOL="heat-config-cfn-init"
Configuration data which used to be included in the AWS::CloudFormation::Init section of resource metadata is instead moved to the config property of the config resource, as in the following example:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 | resources:
config:
type: OS::Heat::StructuredConfig
properties:
group: cfn-init
inputs:
- name: bar
config:
config:
files:
/tmp/foo:
content:
get_input: bar
mode: '000644'
deployment:
type: OS::Heat::StructuredDeployment
properties:
name: 10_deployment
signal_transport: NO_SIGNAL
config:
get_resource: config
server:
get_resource: server
input_values:
bar: baaaaa
other_deployment:
type: OS::Heat::StructuredDeployment
properties:
name: 20_other_deployment
signal_transport: NO_SIGNAL
config:
get_resource: config
server:
get_resource: server
input_values:
bar: barmy
server:
type: OS::Nova::Server
properties:
image: {get_param: image}
flavor: {get_param: flavor}
key_name: {get_param: key_name}
user_data_format: SOFTWARE_CONFIG
|
There are a number of things to note about this template example:
The puppet hook makes it possible to write configuration as puppet manifests which are deployed and run in a masterless environment.
To specify configuration as puppet manifests the heat-config-puppet element is required to be on the built image, so Custom image script needs to be modified with the following:
export DEPLOYMENT_TOOL="heat-config-puppet"
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 | resources:
config:
type: OS::Heat::SoftwareConfig
properties:
group: puppet
inputs:
- name: foo
- name: bar
outputs:
- name: result
config:
get_file: example-puppet-manifest.pp
deployment:
type: OS::Heat::SoftwareDeployment
properties:
config:
get_resource: config
server:
get_resource: server
input_values:
foo: fooooo
bar: baaaaa
server:
type: OS::Nova::Server
properties:
image: {get_param: image}
flavor: {get_param: flavor}
key_name: {get_param: key_name}
user_data_format: SOFTWARE_CONFIG
outputs:
result:
value:
get_attr: [deployment, result]
stdout:
value:
get_attr: [deployment, deploy_stdout]
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This demonstrates the use of the get_file function, which will attach the contents of the file example-puppet-manifest.pp, containing:
1 2 3 4 5 6 7 8 9 10 11 12 13 | file { 'barfile':
ensure => file,
mode => '0644',
path => '/tmp/$::bar',
content => '$::foo',
}
file { 'output_result':
ensure => file,
path => '$::heat_outputs_path.result',
mode => '0644',
content => 'The file /tmp/$::bar contains $::foo',
}
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