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Startup Script Library

This terraform module provides a mechanism to store a library of bash functions intended for use in startup scripts. The goal is to have a single place to add functionality useful by all instances.

Use cases are:

  • Logging functions
  • Debugging functions
  • Functions to execute commands and provide a consistent output format for the end user and/or machine parsing via logs.

Compatibility

This module is meant for use with Terraform 0.12. If you haven't upgraded and need a Terraform 0.11.x-compatible version of this module, the last released version intended for Terraform 0.11.x is 0.1.0.

Usage

The library is loaded as the startup script of an instance. It initializes and passes control to the metadata key startup-script-custom. Control is passed using bash's source mechanism so that all functions provided by the library are available.

Add the following to your Terraform module. Update the tag as necessary.

module "startup-script-lib" {
  source = "git::https://github.com/terraform-google-modules/terraform-google-startup-scripts.git?ref=v0.1.0"
}

When managing a compute instance, your module is responsible for passing the library of functions as a string values of the startup-script metadata key. Your module may also pass configuration via the startup-script-config metadata key. Inject the library into the compute instance by reading the output content like so:

resource "google_compute_instance" "example" {
  # other attributes removed
  metadata {
    startup-script        = "${module.startup-script-lib.content}"
    startup-script-custom = "stdlib::info Hello World"
  }
}

Features

Configuration of startup-script

This module provides a mechanism to automatically load configuration values for use by startup-script-custom. Configuration values are automatically sourced from the metadata key instance/attributes/startup-script-config. This module follows the /etc/sysconfig/defaults model of loading configuration keys and values.

Set the startup-script-config metadata key to a rendered template:

# IPIP peer address configuration.
PEER_OUTER_IPADDR='${peer_outer_ipaddr}'
PEER_INNER_IPADDR='${peer_inner_ipaddr}'
MY_INNER_IPADDR='${my_inner_ipaddr}'
# Subnets to route through the IPIP Tunnel to the peer
IPIP_SUBNETS='${ipip_subnets}'

Fill in this template in Terraform:

data "template_file" "startup_script_config" {
  template = "${file("${path.module}/templates/startup-script-config.tpl")}"
  vars {
    peer_outer_ipaddr = "${var.peer_outer_ipaddr}"
    peer_inner_ipaddr = "${var.peer_inner_ipaddr}"
    my_inner_ipaddr   = "${var.my_inner_ipaddr}"
    ipip_subnets      = "${var.ipip_subnets}"
  }
}

These configuration values will be automatically loaded into the environment when startup-script-custom script executes.

Behavior

Updating vs Deleting instances

Note the use of of the compute_instance metadata attribute causes existing instances to be updated in place when values change. In contrast, the use of the metadata_startup_script attribute causes Terraform to delete and re-create the instance as per the compute_instance metadata_startup_script documentation.

Re-run startup scripts

It can be helpful to re-run custom startup scripts by logging into the instance and running.

sudo google_metadata_script_runner --script-type startup

To enable full debugging, both in the script runner and the startup script library, set DEBUG to a non-zero length string.

sudo DEBUG=1 google_metadata_script_runner --script-type startup --debug

Configuration

The behavior of the startup scripts library is governed by environment variables. Feature flags are enabled by setting the environment variable to a non-zero length value. Logs are sent to syslog and standard error by default.

Variable Default Description
DEBUG unset Log debug messages if set.
QUIET unset Silence log messages if set.
COLOR unset Colored logs if set.
DATE_FMT Log date +<format>.
SYSLOG_DEBUG_PRIORITY syslog.debug logger -p <value>
SYSLOG_INFO_PRIORITY syslog.info logger -p <value>
SYSLOG_ERROR_PRIORITY syslog.error logger -p <value>
VARDIR /var/lib/startup Durable alternative to TMPDIR

Automated Tests

Automated tests are run inside of a docker image. The initial tests are modeled as specification tests validating expected behavior. bats is the test framework run inside the container.

Spec Tests

Build the bats container image

Build the image used to validate specification tests. This command builds an image with bats installed, suitable for running the tests.

make docker_build_bats

Validate Behavior Specifications

Validate the expected behavior using the image containing the bats tools. This command runs the container and executes bats against each of the test suite files in test/spec/

make docker_bats

Example output:

1..4
ok 1 STARTUP_SCRIPT_STDLIB_INITIALIZED is initialized to 0
ok 2 E_RUN_OR_DIE error code is 5
ok 3 E_MISSING_MANDATORY_ARG error code is 9
ok 4 E_UNKNOWN_ARG error code is 10

Inputs

Name Description Type Default Required
enable_get_from_bucket If not false, include stdlib::get_from_bucket() prior to executing startup-script-custom. Requires gsutil in the PATH. See also enable_init_gsutil_crcmod_el feature flag. bool "false" no
enable_init_gsutil_crcmod_el If not false, include stdlib::init_gsutil_crcmod_el() prior to executing startup-script-custom. Call this function from startup-script-custom to initialize gsutil as per https://cloud.google.com/storage/docs/gsutil/addlhelp/CRC32CandInstallingcrcmod#centos-rhel-and-fedora Intended for CentOS, RHEL and Fedora systems. bool "false" no
enable_setup_init_script If not false, include stdlib::setup_init_script() prior to executing startup-script-custom. Call this function to load an init script from GCS into /etc/init.d and initialize it with chkconfig. This function depends on stdlib::get_from_bucket, so this function won't be enabled if enable_get_from_bucket is false. bool "false" no
enable_setup_sudoers If true, include stdlib::setup_sudoers() prior to executing startup-script-custom. Call this function from startup-script-custom to setup unix usernames in sudoers Comma separated values must be posted to the project metadata key project/attributes/sudoers bool "false" no

Outputs

Name Description
content startup-script-stdlib.sh content as a string value.