This module allows creating a managed instance group supporting one or more application versions via instance templates. Optionally, a health check and an autoscaler can be created, and the managed instance group can be configured to be stateful.
This module can be coupled with the [`compute-vm`](../compute-vm) module which can manage instance templates, and the [`net-ilb`](../net-ilb) module to assign the MIG to a backend wired to an Internal Load Balancer. The first use case is shown in the examples below.
Stateful disks can be created directly, as shown in the last example below.
This example shows how to manage a simple MIG that leverages the `compute-vm` module to manage the underlying instance template. The following sub-examples will only show how to enable specific features of this module, and won't replicate the combined setup.
If multiple versions are desired, use more `compute-vm` instances for the additional templates used in each version (not shown here), and reference them like this:
The module can create and manage an autoscaler associated with the MIG. When using autoscaling do not set the `target_size` variable or set it to `null`. Here we show a CPU utilization autoscaler, the other available modes are load balancing utilization and custom metric, like the underlying autoscaler resource.
Stateful MIGs have some limitations documented [here](https://cloud.google.com/compute/docs/instance-groups/configuring-stateful-migs#limitations). Enforcement of these requirements is the responsibility of users of this module.
You can configure a disk defined in the instance template to be stateful for all instances in the MIG by configuring in the MIG's stateful policy, using the `stateful_disk_mig` variable. Alternatively, you can also configure stateful persistent disks individually per instance of the MIG by setting the `stateful_disk_instance` variable. A discussion on these scenarios can be found in the [docs](https://cloud.google.com/compute/docs/instance-groups/configuring-stateful-disks-in-migs).
An example using only the configuration at the MIG level can be seen below.
Note that when referencing the stateful disk, you use `device_name` and not `disk_name`.
| [default_version](variables.tf#L45) | Default application version template. Additional versions can be specified via the `versions` variable. | <codetitle="object({ instance_template = string name = string })">object({…})</code> | ✓ | |
| [location](variables.tf#L64) | Compute zone, or region if `regional` is set to true. | <code>string</code> | ✓ | |
| [auto_healing_policies](variables.tf#L17) | Auto-healing policies for this group. | <codetitle="object({ health_check = string initial_delay_sec = number })">object({…})</code> | | <code>null</code> |
| [autoscaler_config](variables.tf#L26) | Optional autoscaler configuration. Only one of 'cpu_utilization_target' 'load_balancing_utilization_target' or 'metric' can be not null. | <codetitle="object({ max_replicas = number min_replicas = number cooldown_period = number cpu_utilization_target = number load_balancing_utilization_target = number metric = object({ name = string single_instance_assignment = number target = number type = string # GAUGE, DELTA_PER_SECOND, DELTA_PER_MINUTE filter = string }) })">object({…})</code> | | <code>null</code> |
| [health_check_config](variables.tf#L53) | Optional auto-created health check configuration, use the output self-link to set it in the auto healing policy. Refer to examples for usage. | <codetitle="object({ type = string # http https tcp ssl http2 check = map(any) # actual health check block attributes config = map(number) # interval, thresholds, timeout logging = bool })">object({…})</code> | | <code>null</code> |
| [regional](variables.tf#L84) | Use regional instance group. When set, `location` should be set to the region. | <code>bool</code> | | <code>false</code> |
| [stateful_config](variables.tf#L90) | Stateful configuration can be done by individual instances or for all instances in the MIG. They key in per_instance_config is the name of the specific instance. The key of the stateful_disks is the 'device_name' field of the resource. Please note that device_name is defined at the OS mount level, unlike the disk name. | <codetitle="object({ per_instance_config = map(object({ stateful_disks = map(object({ source = string mode = string # READ_WRITE | READ_ONLY delete_rule = string # NEVER | ON_PERMANENT_INSTANCE_DELETION })) metadata = map(string) update_config = object({ minimal_action = string # NONE | REPLACE | RESTART | REFRESH most_disruptive_allowed_action = string # REPLACE | RESTART | REFRESH | NONE remove_instance_state_on_destroy = bool }) })) mig_config = object({ stateful_disks = map(object({ delete_rule = string # NEVER | ON_PERMANENT_INSTANCE_DELETION })) }) })">object({…})</code> | | <code>null</code> |
| [target_pools](variables.tf#L121) | Optional list of URLs for target pools to which new instances in the group are added. | <code>list(string)</code> | | <code>[]</code> |
| [target_size](variables.tf#L127) | Group target size, leave null when using an autoscaler. | <code>number</code> | | <code>null</code> |
| [update_policy](variables.tf#L133) | Update policy. Type can be 'OPPORTUNISTIC' or 'PROACTIVE', action 'REPLACE' or 'restart', surge type 'fixed' or 'percent'. | <codetitle="object({ type = string # OPPORTUNISTIC | PROACTIVE minimal_action = string # REPLACE | RESTART min_ready_sec = number max_surge_type = string # fixed | percent max_surge = number max_unavailable_type = string max_unavailable = number })">object({…})</code> | | <code>null</code> |
