upgrade instructions

UPGRADE.md

@@ -0,0 +1,30 @@
+# Upgrading your AccessTier
+
+This document explains how to upgrade your AccessTier to a newer version with zero downtime.
+
+ 1. (Optional) If you have pinned your deployment to a particular version of Netagent, update the value of `package_name` to match the version you want to deploy.
+
+    ```hcl
+    module "aws_accesstier" {
+        package_name = "banyan-netagent-1.26.1"
+    }
+    ```
+
+ 2. Run `terraform plan` to confirm that only the auto-scaling group and launch configuration will be updated:
+
+    ```text
+    Terraform will perform the following actions:
+
+    # aws_autoscaling_group.asg will be updated in-place
+    # aws_launch_configuration.conf must be replaced
+    ```
+
+ 3. Run `terraform apply` to update the ASG and launch configuration.
+
+ 4. Open the AWS management console in your browser. Navigate to **EC2 > Auto-Scaling Groups** and select your ASG. Click on **Instance refresh**.
+
+ 5. Click the **Start instance refresh** button. Change the minimum healthy percentage to 50% and the instance warmup time to 180 seconds. Click **Start**.
+
+ 6. After a few minutes, the status of the instance refresh should change to "Successful". 
+
+ 7. Log into the Banyan Command Center to verify that the new AccessTier instances are reporting. Navigate to **Directory & Infrastructure > AccessTiers** to see them.