StackGroup Config¶
StackGroup config stores information related to the StackGroup, such as a
particular profile to use, the name of the S3 bucket in which to store
templates, and the target region in which to build resources. StackGroup config
is stored in various files around the directory structure, all with the name
config.yaml
.
Structure¶
An StackGroup config file is a yaml object of key-value pairs configuring Sceptre. The available keys are listed below.
project_code (required)
region (required)
profile optional
required_version (optional)
template_bucket_name (optional)
template_key_prefix (optional)
j2_environment (optional)
http_template_handler (optional)
Sceptre will only check for and uses the above keys in StackGroup config files
and are directly accessible from Stack(). Any other keys added by the user are
made available via stack_group_confg
attribute on Stack()
.
profile¶
The name of the profile as defined in ~/.aws/config
and
~/.aws/credentials
. Use the aws configure –profile <profile_id> command
form the AWS CLI to add profiles to these files.
Reference: AWS_CLI_Configure
project_code¶
A string which is prepended to the Stack names of all Stacks built by Sceptre.
region¶
The AWS region to build Stacks in. Sceptre should work in any region which supports CloudFormation.
template_bucket_name¶
The name of an S3 bucket to upload CloudFormation Templates to. Note that S3
bucket names must be globally unique. If the bucket does not exist, Sceptre
creates one using the given name, in the AWS region specified by region
.
If this parameter is not added, Sceptre does not upload the template to S3, but
supplies the template to Boto3 via the TemplateBody
argument. Templates
supplied in this way have a lower maximum length, so using the
template_bucket_name
parameter is recommended.
template_key_prefix¶
A string which is prefixed onto the key used to store templates uploaded to S3. Templates are stored using the key:
<template_key_prefix>/<region>/<stack_group>/<stack_name>-<timestamp>.<extension>
Template key prefix can contain slashes (“/”), which are displayed as directories in the S3 console.
Extension can be json
or yaml
.
Note that if template_bucket_name
is not supplied, this parameter is
ignored.
j2_environment¶
A dictionary that is combined with the default jinja2 environment. It’s converted to keyword arguments then passed to [jinja2.Environment](https://jinja.palletsprojects.com/en/2.11.x/api/#jinja2.Environment). This will impact Templating of stacks by modifying the behavior of jinja.
j2_environment:
extensions:
- jinja2.ext.i18n
- jinja2.ext.do
lstrip_blocks: True
trim_blocks: True
newline_sequence: \n
http_template_handler¶
- Options passed to the http template handler.
retries - The number of retry attempts (default is 5)
timeout - The timeout for the session in seconds (default is 5)
http_template_handler:
retries: 10
timeout: 20
Cascading Config¶
Using Sceptre, config files are cascaded. Given the following sceptre directory structure:
.
└── config
├── account-1
│ ├── config.yaml
│ └── dev
│ └── config.yaml
└── config.yaml
General configurations should be defined at a high level, and more specific configurations should be defined at a lower directory level.
YAML files that define configuration settings with conflicting keys, the child configuration file will take precedence.
In the above directory structure, config/config.yaml
will be read in first,
followed by config/account-1/config.yaml
, followed by
config/account-1/dev/config.yaml
.
For example, if you wanted the dev
StackGroup to build to a different
region, this setting could be specified in the config/dev/config.yaml
file,
and would only be applied to builds in the dev
StackGroup.
Templating¶
Sceptre supports the use of templating in config files. Templating allows
config files to be further configured using values from the command line,
environment variables, files or parts of the command_path
.
Internally, Sceptre uses Jinja2 for templating, so any valid Jinja2 syntax should work with Sceptre templating.
Templating can be used for any values in the config files, not just those that are used by Sceptre.
Var¶
User variables are used to replace the value of any item in a config file with a value defined by a CLI flag or in a YAML variable file:
profile: {{ var.profile }}
region: eu-west-1
This item can be set using either a command line flag:
sceptre --var "profile=<your profile>" <COMMAND>
Or from a YAML variable file:
sceptre --var-file=variables.yaml <COMMAND>
where variables.yaml
contains:
profile: <your profile>
Both the --var
and --var-file
flags can be used multiple times. If
multiple --var-file
options are supplied, the variables from these files
will be merged, with a higher precedence given to options specified later in
the command. Values supplied using --var
take the highest precedence and
will overwrite any value defined in the variable files.
For example if we have the following variable files:
# default.yaml
region: eu-west-1
profile: dev
project_code: api
# prod.yaml
profile: prod
The following sceptre command:
sceptre --var-file=default.yaml --var-file=prod.yaml --var region=us-east-1 <COMMAND>
Will result in the following variables being available to the jinja templating:
region: us-east-1
profile: prod
project_code: api
Note that by default, dictionaries are not merged. If the variable appearing in the last variable file is a dictionary, and the same variable is defined in an earlier variable file, that whole dictionary will be overwritten. For example, this would not work as intended:
# default.yaml
tags: {"Env": "dev", "Project": "Widget"}
# prod.yaml
tags: {"Env": "prod"}
Rather, the final dictionary would only contain the Env
key.
By using the --merge-vars
option, these tags can be merged as intended:
sceptre --merge-vars --var-file=default.yaml --var-file=prod.yaml --var region=us-east-1 <COMMAND>
This will result in the following:
tags: {"Env": "prod", "Project": "Widget"}
For command line flags, Sceptre splits the string on the first equals sign “=”, and sets the key to be the first substring, and the value to be the second. Due to the large number of possible user inputs, no error checking is performed on the value of the –var flag, and it is the user’s responsibility to make sure that the value is correctly formatted.
All user variables are supplied to all config files, so users must be careful to make sure that user variable names do not unintentionally clash.
Environment Variables¶
Config item values can be replaced with environment variables:
profile: {{ environment_variable.PROFILE }}
region: eu-west-1
Where PROFILE
is the name of an environment variable.
Command Path¶
Config item values can be replaced with parts of the command_path
region: {{ command_path.0 }}
profile: default
Where the value is taken from the first part of the command_path
from the
invoking sceptre command:
sceptre launch eu-west-1/dev/vpc.yaml
Template Defaults¶
Any templated value can be supplied with a default value with the syntax:
{{ var.value | default("default_value") }}
Examples¶
profile: profile
project_code: prj
region: eu-west-1
template_bucket_name: sceptre-artifacts
template_key_prefix: my/prefix
profile: {{ var.profile }}
project_code: {{ var.project_code | default("prj") }}
region: {{ command_path.2 }}
template_bucket_name: {{ environment_variable.TEMPLATE_BUCKET_NAME }}