Repository: gruntwork-io/kubergrunt (go)

Issue:
Fault tolerance in the eks deploy command
The eks deploy command should track where it is in the state of the deployment and recover from failures.

For example, it is fairly painful to recoup if the `deploy` command fails after the ASG was expanded and during the drain call. In that failure mode, the user has to manually drain all the nodes, and then terminate them. We should figure out a way for the `deploy` command to remember where it failed, and then provide the ability to retry starting from that step.

Pull request description:
Fault tolerance for eks deploy
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## Description

This PR introduces fault tolerance for the `eks deploy` subcommand by introducing a recovery file for storing deploy state.
The `eks deploy` is split into multiple stages and the state file is updated after each stage:

1. Gather ASG info: Retrieve the ASG object and gather required info
2. Set ASG max capacity: Make sure there is enough max size capacity to scale up
3. Scale up: Launching new nodes with new launch config
4. Wait for new nodes: Wait for new nodes to be ready and verify everything is OK in k8s
5. Cordon nodes: Cordon old instances in cluster ASG
6. Drain nodes: Drain Pods on old instances
7. Detach instances: Remove old nodes from ASG
8. Terminate instances: Terminating detached instances
9. Restore ASG max capacity: Restore the ASG into original max capacity

The state file is generated into the working directory `./.kubergrunt.state` and persisted after each successful stage. If the `eks deploy` command fails for some reason, execution resumes from the last successful state. The existing recovery file can also be ignored with the `--ignore-recovery-file` flag. In this case the recovery file will be re-initialized.

The state is implemented with simple boolean flags instead of a state machine library. The stages in `eks deploy` are linear and there is no complex state handling, so a state machine library seemed overkill.

To better modularity and keeping action and verification stages separate, the `scaleUp` function is split into actual scale up and verification functions. This allows safer re-execution in case scale up was successful but verification fails for some reason.

### Other notable things

- Removing `defer setAsgMaxSize` and moving that to the last stage. If we're retrying using the recovery file, the original `defer` functionality could potentially lead to unexpected behaviour. I'm open for discussion on this, though.

- Kubernetes `drain` and `cordon` operations are still executed for the whole set of existing nodes - I assume these are idempotent and can safely be executed multiple times.

- As the AWS operations for detaching and terminating instances are batched, the command can still fail if previous detach, for example, was a partial success. Same applies to termination. Don't necessarily think this will be an issue


### Documentation

- README updated
- cli option documented

## TODOs

- [x] Ensure the branch is named correctly with the issue number. e.g: `feature/new-vpc-endpoints-955` or `bug/missing-count-param-434`.
- [x] Update the docs.
- [x] Keep the changes backwards compatible where possible.
- [x] Run the pre-commit checks successfully.
- [x] Run the relevant tests successfully.
- [x] Ensure any 3rd party code adheres with our license policy: https://www.notion.so/gruntwork/Gruntwork-licenses-and-open-source-usage-policy-f7dece1f780341c7b69c1763f22b1378
- [ ] _Maintainers Only._ If necessary, release a new version of this repo.
- [ ] _Maintainers Only._ If there were backwards incompatible changes, include a migration guide in the release notes.
- [ ] _Maintainers Only._ Add to the next version of the monthly newsletter (see https://www.notion.so/gruntwork/Monthly-Newsletter-9198cbe7f8914d4abce23dca7b435f43).


## Related Issues

Fixes #109 


Patch:
diff --git a/CODEOWNERS b/CODEOWNERS
index 7430248..d955c7b 100644
--- a/CODEOWNERS
+++ b/CODEOWNERS
@@ -1,1 +1,1 @@
-* @yorinasub17 @bwhaley @rhoboat @zackproser @autero1
+* @yorinasub17 @rhoboat @zackproser @autero1
diff --git a/README.md b/README.md
index c3f46ad..8b166f5 100644
--- a/README.md
+++ b/README.md
@@ -256,6 +256,15 @@ Currently `kubergrunt` does not implement any checks for these resources to be i
 plan to bake in checks into the deployment command to verify that all services have a disruption budget set, and warn
 the user of any services that do not have a check.
 
+**`eks deploy` recovery file**
+
+Due to the nature of rolling update, the `deploy` subcommand performs multiple sequential actions that 
+depend on success of the previous operations. To mitigate intermittent failures, the `deploy` subcommand creates a
+recovery file in the working directory for storing current deploy state. The recovery file is updated after 
+each stage and if the `deploy` subcommand fails for some reason, execution resumes from the last successful state.
+The existing recovery file can also be ignored with the `--ignore-recovery-file` flag. In this case the recovery 
+file will be re-initialized.
+
 #### sync-core-components
 
 This subcommand will sync the core components of an EKS cluster to match the deployed Kubernetes version by following
diff --git a/cmd/eks.go b/cmd/eks.go
index e183cd6..e2f84e0 100644
--- a/cmd/eks.go
+++ b/cmd/eks.go
@@ -24,6 +24,10 @@ var (
 		Name:  "wait",
 		Usage: "Whether or not to wait for the command to succeed.",
 	}
+	ignoreRecoveryFileFlag = cli.BoolFlag{
+		Name:  "ignore-recovery-file",
+		Usage: "Ignore existing recovery file and start deploy process from the beginning.",
+	}
 	eksKubectlContextNameFlag = cli.StringFlag{
 		Name:  KubectlContextNameFlagName,
 		Usage: "The name to use for the config context that is set up to authenticate with the EKS cluster. Defaults to the cluster ARN.",
@@ -230,6 +234,8 @@ Note that to minimize service disruption from this command, your services should
 This command includes retry loops for certain stages (e.g waiting for the ASG to scale up). This retry loop is configurable with the options --max-retries and --sleep-between-retries. The command will try up to --max-retries times, sleeping for the duration specified by --sleep-between-retries inbetween each failed attempt.
 
 If max-retries is unspecified, this command will use a value that translates to a total wait time of 5 minutes per wave of ASG, where each wave is 10 instances. For example, if the number of instances in the ASG is 15 instances, this translates to 2 waves, which leads to a total wait time of 10 minutes. To achieve a 10 minute wait time with the default sleep between retries (15 seconds), the max retries needs to be set to 40.
+
+As the deploy command contains multiple stages, this command also generates a recovery file (.kubergrunt.state) containing the current deploy state in the working directory. The state file is used to resume the deploy operation from the point of failure, and is automatically deleted upon completion of the command. You can optionally ignore the state file with --ignore-recovery-file flag, which will generate a new recovery file.
 `,
 				Action: rollOutDeployment,
 				Flags: []cli.Flag{
@@ -245,6 +251,7 @@ If max-retries is unspecified, this command will use a value that translates to
 					deleteLocalDataFlag,
 					waitMaxRetriesFlag,
 					waitSleepBetweenRetriesFlag,
+					ignoreRecoveryFileFlag,
 				},
 			},
 			cli.Command{
@@ -405,6 +412,7 @@ func rollOutDeployment(cliContext *cli.Context) error {
 
 	drainTimeout := cliContext.Duration(drainTimeoutFlag.Name)
 	deleteLocalData := cliContext.Bool(deleteLocalDataFlag.Name)
+	ignoreRecoveryFile := cliContext.Bool(ignoreRecoveryFileFlag.Name)
 	waitMaxRetries := cliContext.Int(waitMaxRetriesFlag.Name)
 	waitSleepBetweenRetries := cliContext.Duration(waitSleepBetweenRetriesFlag.Name)
 
@@ -416,6 +424,7 @@ func rollOutDeployment(cliContext *cli.Context) error {
 		deleteLocalData,
 		waitMaxRetries,
 		waitSleepBetweenRetries,
+		ignoreRecoveryFile,
 	)
 }
 
diff --git a/eks/asg.go b/eks/asg.go
index 02f4046..b920a66 100644
--- a/eks/asg.go
+++ b/eks/asg.go
@@ -32,51 +32,67 @@ func GetAsgByName(svc *autoscaling.AutoScaling, asgName string) (*autoscaling.Gr
 	return groups[0], nil
 }
 
-// scaleUp will scale the ASG up and wait until all the nodes are available. Specifically:
-// - Set the desired capacity on the ASG
-// - Wait for the capacity in the ASG to meet the desired capacity (instances are launched)
-// - Wait for the new instances to be ready in Kubernetes
-// - Wait for the new instances to be registered with external load balancers
+// scaleUp will scale the ASG up, wait until all the nodes are available and return new instance IDs.
 func scaleUp(
 	asgSvc *autoscaling.AutoScaling,
-	ec2Svc *ec2.EC2,
-	elbSvc *elb.ELB,
-	elbv2Svc *elbv2.ELBV2,
-	kubectlOptions *kubectl.KubectlOptions,
 	asgName string,
+	originalInstanceIds []string,
 	desiredCapacity int64,
-	oldInstanceIds []string,
 	maxRetries int,
 	sleepBetweenRetries time.Duration,
-) error {
+) ([]string, error) {
 	logger := logging.GetProjectLogger()
+
 	err := setAsgCapacity(asgSvc, asgName, desiredCapacity)
 	if err != nil {
 		logger.Errorf("Failed to set ASG capacity to %d", desiredCapacity)
 		logger.Errorf("If the capacity is set in AWS, undo by lowering back to the original capacity. If the capacity is not yet set, triage the error message below and try again.")
-		return err
+		return nil, err
 	}
+
+	// All of the following are read operations and do not affect the state, so it's safe to run these
+	// each time we execute
 	err = waitForCapacity(asgSvc, asgName, maxRetries, sleepBetweenRetries)
 	if err != nil {
 		logger.Errorf("Timed out waiting for ASG to reach steady state.")
-		// TODO: can we use stages to pick up from here?
 		logger.Errorf("Undo by terminating all the new instances and trying again")
-		return err
+		return nil, err
 	}
-	newInstanceIds, err := getLaunchedInstanceIds(asgSvc, asgName, oldInstanceIds)
+
+	newInstanceIds, err := getLaunchedInstanceIds(asgSvc, asgName, originalInstanceIds)
 	if err != nil {
 		logger.Errorf("Error retrieving information about the ASG")
 		// TODO: can we use stages to pick up from here?
 		logger.Errorf("Undo by terminating all the new instances and trying again")
-		return err
+		return nil, err
 	}
-	instances, err := instanceDetailsFromIds(ec2Svc, newInstanceIds)
+
+	return newInstanceIds, nil
+}
+
+// waitAndVerifyNewInstances will scale the ASG up and wait until all the nodes are available. Specifically:
+// - Wait for the capacity in the ASG to meet the desired capacity (instances are launched)
+// - Wait for the new instances to be ready in Kubernetes
+// - Wait for the new instances to be registered with external load balancers
+func waitAndVerifyNewInstances(
+	ec2Svc *ec2.EC2,
+	elbSvc *elb.ELB,
+	elbv2Svc *elbv2.ELBV2,
+	instanceIds []string,
+	kubectlOptions *kubectl.KubectlOptions,
+	maxRetries int,
+	sleepBetweenRetries time.Duration,
+) error {
+	logger := logging.GetProjectLogger()
+
+	instances, err := instanceDetailsFromIds(ec2Svc, instanceIds)
 	if err != nil {
 		logger.Errorf("Error retrieving detailed about the instances")
 		// TODO: can we use stages to pick up from here?
 		logger.Errorf("Undo by terminating all the new instances and trying again")
 		return err
 	}
+
 	eksKubeNodeNames := kubeNodeNamesFromInstances(instances)
 	err = kubectl.WaitForNodesReady(
 		kubectlOptions,
@@ -86,21 +102,18 @@ func scaleUp(
 	)
 	if err != nil {
 		logger.Errorf("Timed out waiting for the instances to reach ready state in Kubernetes.")
-		// TODO: can we use stages to pick up from here?
 		logger.Errorf("Undo by terminating all the new instances and trying again")
 		return err
 	}
 	elbs, err := kubectl.GetAWSLoadBalancers(kubectlOptions)
 	if err != nil {
 		logger.Errorf("Error retrieving associated ELB names of the Kubernetes services.")
-		// TODO: can we use stages to pick up from here?
 		logger.Errorf("Undo by terminating all the new instances and trying again")
 		return err
 	}
-	err = waitForAnyInstancesRegisteredToELB(elbSvc, elbv2Svc, elbs, newInstanceIds)
+	err = waitForAnyInstancesRegisteredToELB(elbSvc, elbv2Svc, elbs, instanceIds)
 	if err != nil {
 		logger.Errorf("Timed out waiting for the instances to register to the Service ELBs.")
-		// TODO: can we use stages to pick up from here?
 		logger.Errorf("Undo by terminating all the new instances and trying again")
 		return err
 	}
diff --git a/eks/deploy.go b/eks/deploy.go
index a8e540e..b63ee5b 100644
--- a/eks/deploy.go
+++ b/eks/deploy.go
@@ -2,7 +2,6 @@ package eks
 
 import (
 	"math"
-	"strings"
 	"time"
 
 	"github.com/aws/aws-sdk-go/service/autoscaling"
@@ -16,12 +15,6 @@ import (
 	"github.com/gruntwork-io/kubergrunt/logging"
 )
 
-type asgInfo struct {
-	originalCapacity   int64
-	maxSize            int64
-	currentInstanceIDs []string
-}
-
 // RollOutDeployment will perform a zero downtime roll out of the current launch configuration associated with the
 // provided ASG in the provided EKS cluster. This is accomplished by:
 // 1. Double the desired capacity of the Auto Scaling Group that powers the EKS Cluster. This will launch new EKS
@@ -32,7 +25,7 @@ type asgInfo struct {
 //    rescheduled on the new EKS workers.
 // 5. Wait for all the pods to migrate off of the old EKS workers.
 // 6. Set the desired capacity down to the original value and remove the old EKS workers from the ASG.
-// TODO feature request: Break up into stages/checkpoints, and store state along the way so that command can pick up
+// The process is broken up into stages/checkpoints, state is stored along the way so that command can pick up
 // from a stage if something bad happens.
 func RollOutDeployment(
 	region string,
@@ -42,6 +35,7 @@ func RollOutDeployment(
 	deleteLocalData bool,
 	maxRetries int,
 	sleepBetweenRetries time.Duration,
+	ignoreRecoveryFile bool,
 ) (returnErr error) {
 	logger := logging.GetProjectLogger()
 	logger.Infof("Beginning roll out for EKS cluster worker group %s in %s", eksAsgName, region)
@@ -57,134 +51,66 @@ func RollOutDeployment(
 	elbv2Svc := elbv2.New(sess)
 	logger.Infof("Successfully authenticated with AWS")
 
-	// Retrieve the ASG object and gather required info we will need later
-	asgInfo, err := getAsgInfo(asgSvc, eksAsgName)
+	stateFile := defaultStateFile
+
+	// Retrieve state if one exists or construct a new one
+	state, err := initDeployState(stateFile, ignoreRecoveryFile, maxRetries, sleepBetweenRetries)
 	if err != nil {
 		return err
 	}
 
-	// Calculate default max retries
-	if maxRetries == 0 {
-		maxRetries = getDefaultMaxRetries(asgInfo.originalCapacity, sleepBetweenRetries)
-		logger.Infof(
-			"No max retries set. Defaulted to %d based on sleep between retries duration of %s and scale up count %d.",
-			maxRetries,
-			sleepBetweenRetries,
-			asgInfo.originalCapacity,
-		)
+	err = state.gatherASGInfo(asgSvc, []string{eksAsgName})
+	if err != nil {
+		return err
 	}
 
-	// Make sure ASG is in steady state
-	if asgInfo.originalCapacity != int64(len(asgInfo.currentInstanceIDs)) {
-		logger.Infof("Ensuring ASG is in steady state (current capacity = desired capacity)")
-		err = waitForCapacity(asgSvc, eksAsgName, maxRetries, sleepBetweenRetries)
-		if err != nil {
-			logger.Error("Error waiting for ASG to reach steady state. Try again after the ASG is in a steady state.")
-			return err
-		}
-		logger.Infof("Verified ASG is in steady state (current capacity = desired capacity)")
-		asgInfo, err = getAsgInfo(asgSvc, eksAsgName)
-		if err != nil {
-			return err
-		}
+	err = state.setMaxCapacity(asgSvc)
+	if err != nil {
+		return err
 	}
 
-	// Make sure there is enough max size capacity to scale up
-	maxCapacityForUpdate := asgInfo.originalCapacity * 2
-	if asgInfo.maxSize < maxCapacityForUpdate {
-		// Make sure we attempt to restore the original ASG max size at the end of the function, regardless of error.
-		defer func() {
-			err := setAsgMaxSize(asgSvc, eksAsgName, asgInfo.maxSize)
-			// Only return error from this routine if we are not already bubbling an error back from previous calls in
-			// the function.
-			if err != nil && returnErr == nil {
-				returnErr = err
-			}
-		}()
-
-		// Update the ASG max size to have enough capacity to handle the update.
-		err := setAsgMaxSize(asgSvc, eksAsgName, maxCapacityForUpdate)
-		if err != nil {
-			return err
-		}
+	err = state.scaleUp(asgSvc)
+	if err != nil {
+		return err
 	}
 
-	logger.Infof("Starting with the following list of instances in ASG:")
-	logger.Infof("%s", strings.Join(asgInfo.currentInstanceIDs, ","))
-
-	logger.Infof("Launching new nodes with new launch config on ASG %s", eksAsgName)
-	err = scaleUp(
-		asgSvc,
-		ec2Svc,
-		elbSvc,
-		elbv2Svc,
-		kubectlOptions,
-		eksAsgName,
-		maxCapacityForUpdate,
-		asgInfo.currentInstanceIDs,
-		maxRetries,
-		sleepBetweenRetries,
-	)
+	err = state.waitForNodes(ec2Svc, elbSvc, elbv2Svc, kubectlOptions)
 	if err != nil {
 		return err
 	}
-	logger.Infof("Successfully launched new nodes with new launch config on ASG %s", eksAsgName)
 
-	logger.Infof("Cordoning old instances in cluster ASG %s to prevent Pod scheduling", eksAsgName)
-	err = cordonNodesInAsg(ec2Svc, kubectlOptions, asgInfo.currentInstanceIDs)
+	err = state.cordonNodes(ec2Svc, kubectlOptions)
 	if err != nil {
-		logger.Errorf("Error while cordoning nodes.")
-		logger.Errorf("Continue to cordon nodes that failed manually, and then terminate the underlying instances to complete the rollout.")
 		return err
 	}
-	logger.Infof("Successfully cordoned old instances in cluster ASG %s", eksAsgName)
 
-	logger.Infof("Draining Pods on old instances in cluster ASG %s", eksAsgName)
-	err = drainNodesInAsg(ec2Svc, kubectlOptions, asgInfo.currentInstanceIDs, drainTimeout, deleteLocalData)
+	err = state.drainNodes(ec2Svc, kubectlOptions, drainTimeout, deleteLocalData)
 	if err != nil {
-		logger.Errorf("Error while draining nodes.")
-		logger.Errorf("Continue to drain nodes that failed manually, and then terminate the underlying instances to complete the rollout.")
 		return err
 	}
-	logger.Infof("Successfully drained all scheduled Pods on old instances in cluster ASG %s", eksAsgName)
 
-	logger.Infof("Removing old nodes from ASG %s", eksAsgName)
-	err = detachInstances(asgSvc, eksAsgName, asgInfo.currentInstanceIDs)
+	err = state.detachInstances(asgSvc)
 	if err != nil {
-		logger.Errorf("Error while detaching the old instances.")
-		logger.Errorf("Continue to detach the old instances and then terminate the underlying instances to complete the rollout.")
 		return err
 	}
-	err = terminateInstances(ec2Svc, asgInfo.currentInstanceIDs)
+
+	err = state.terminateInstances(ec2Svc)
 	if err != nil {
-		logger.Errorf("Error while terminating the old instances.")
-		logger.Errorf("Continue to terminate the underlying instances to complete the rollout.")
 		return err
 	}
-	logger.Infof("Successfully removed old nodes from ASG %s", eksAsgName)
 
-	logger.Infof("Successfully finished roll out for EKS cluster worker group %s in %s", eksAsgName, region)
-	return nil
-}
+	err = state.restoreCapacity(asgSvc)
+	if err != nil {
+		return err
+	}
 
-// Retrieves current state of the ASG and returns the original Capacity and the IDs of the instances currently
-// associated with it.
-func getAsgInfo(asgSvc *autoscaling.AutoScaling, asgName string) (asgInfo, error) {
-	logger := logging.GetProjectLogger()
-	logger.Infof("Retrieving current ASG info")
-	asg, err := GetAsgByName(asgSvc, asgName)
+	err = state.delete()
 	if err != nil {
-		return asgInfo{}, err
+		logger.Warnf("Error deleting state file %s: %s", stateFile, err.Error())
+		logger.Warn("Remove the file manually")
 	}
-	originalCapacity := *asg.DesiredCapacity
-	maxSize := *asg.MaxSize
-	currentInstances := asg.Instances
-	currentInstanceIDs := idsFromAsgInstances(currentInstances)
-	logger.Infof("Successfully retrieved current ASG info.")
-	logger.Infof("\tCurrent desired capacity: %d", originalCapacity)
-	logger.Infof("\tCurrent max size: %d", maxSize)
-	logger.Infof("\tCurrent capacity: %d", len(currentInstances))
-	return asgInfo{originalCapacity: originalCapacity, maxSize: maxSize, currentInstanceIDs: currentInstanceIDs}, nil
+	logger.Infof("Successfully finished roll out for EKS cluster worker group %s in %s", eksAsgName, region)
+	return nil
 }
 
 // Calculates the default max retries based on a heuristic of 5 minutes per wave. This assumes that the ASG scales up in
diff --git a/eks/deploy_state.go b/eks/deploy_state.go
new file mode 100644
index 0000000..4e18fa5
--- /dev/null
+++ b/eks/deploy_state.go
@@ -0,0 +1,360 @@
+package eks
+
+import (
+	"github.com/aws/aws-sdk-go/service/autoscaling"
+	"github.com/aws/aws-sdk-go/service/ec2"
+	"github.com/aws/aws-sdk-go/service/elb"
+	"github.com/aws/aws-sdk-go/service/elbv2"
+	"github.com/gruntwork-io/go-commons/errors"
+	"github.com/gruntwork-io/kubergrunt/kubectl"
+	"github.com/gruntwork-io/kubergrunt/logging"
+	"github.com/sirupsen/logrus"
+	"io/ioutil"
+	"k8s.io/apimachinery/pkg/util/json"
+	"os"
+	"strings"
+	"time"
+)
+
+// Store the state to current directory by default
+const defaultStateFile = "./.kubergrunt.state"
+
+// DeployState is a basic state machine representing current state of eks deploy subcommand.
+// The entire deploy flow is split into multiple sub-stages and state is persisted after each stage.
+type DeployState struct {
+	GatherASGInfoDone      bool
+	SetMaxCapacityDone     bool
+	ScaleUpDone            bool
+	WaitForNodesDone       bool
+	CordonNodesDone        bool
+	DrainNodesDone         bool
+	DetachInstancesDone    bool
+	TerminateInstancesDone bool
+	RestoreCapacityDone    bool
+
+	Path string
+	ASGs []ASG
+
+	maxRetries          int
+	sleepBetweenRetries time.Duration
+
+	logger *logrus.Entry
+}
+
+// ASG represents the Auto Scaling Group currently being worked on.
+type ASG struct {
+	Name                 string
+	OriginalCapacity     int64
+	MaxCapacityForUpdate int64
+	OriginalMaxCapacity  int64
+	OriginalInstances    []string
+	NewInstances         []string
+}
+
+// initDeployState initializes DeployState struct by either reading existing state file from disk,
+// or if one doesn't exist, create a new one. Does not persist the state to disk.
+func initDeployState(file string, ignoreExistingFile bool, maxRetries int, sleepBetweenRetries time.Duration) (*DeployState, error) {
+	logger := logging.GetProjectLogger()
+	var deployState *DeployState
+
+	if ignoreExistingFile {
+		logger.Info("Ignore existing state file.")
+		deployState = newDeployState(file)
+	} else {
+		logger.Debugf("Looking for existing recovery file %s", file)
+		data, err := ioutil.ReadFile(file)
+		if err != nil {
+			logger.Debugf("No state present, creating new: %s", err.Error())
+			deployState = newDeployState(file)
+		} else {
+			var parsedState DeployState
+			err = json.Unmarshal(data, &parsedState)
+			if err != nil {
+				return nil, err
+			}
+			deployState = &parsedState
+		}
+	}
+
+	deployState.logger = logger
+	deployState.maxRetries = maxRetries
+	deployState.sleepBetweenRetries = sleepBetweenRetries
+
+	return deployState, nil
+}
+
+// persist saves the DeployState struct to disk
+func (state *DeployState) persist() error {
+	file := state.Path
+	state.logger.Debugf("storing state file %s", file)
+
+	data, err := json.Marshal(state)
+
+	if err != nil {
+		return errors.WithStackTrace(err)
+	}
+
+	err = ioutil.WriteFile(file, data, 0644)
+	if err != nil {
+		return errors.WithStackTrace(err)
+	}
+	return nil
+}
+
+// delete deletes the DeployState struct from disk
+func (state *DeployState) delete() error {
+	file := state.Path
+	state.logger.Debugf("Deleting state file %s", file)
+
+	err := os.Remove(file)
+
+	if err != nil {
+		return errors.WithStackTrace(err)
+	}
+
+	return nil
+}
+
+// newDeployState creates an empty DeployState struct
+func newDeployState(path string) *DeployState {
+	return &DeployState{
+		Path: path,
+		ASGs: []ASG{},
+	}
+}
+
+// gatherASGInfo gathers information about the Auto Scaling group currently being worked on. It ensures
+// that the ASG is fully operational with all requested instances running and saves the original configuration
+// (incl. max size, original capacity, instance IDs, etc.) that will be used in subsequent stages
+func (state *DeployState) gatherASGInfo(asgSvc *autoscaling.AutoScaling, eksAsgNames []string) error {
+	if state.GatherASGInfoDone {
+		// Even when we've collected the ASG info, we have to ensure max retries is set
+		state.maxRetries = ensureMaxRetries(state.maxRetries, state.sleepBetweenRetries, state.ASGs[0].OriginalCapacity)
+		state.logger.Debug("ASG Info already gathered - skipping")
+		return nil
+	}
+	eksAsgName := eksAsgNames[0]
+	// Retrieve the ASG object and gather required info we will need later
+	asgInfo, err := getAsgInfo(asgSvc, eksAsgName)
+	if err != nil {
+		return err
+	}
+
+	// Calculate default max retries
+	state.maxRetries = ensureMaxRetries(state.maxRetries, state.sleepBetweenRetries, asgInfo.OriginalCapacity)
+
+	// Make sure ASG is in steady state
+	if asgInfo.OriginalCapacity != int64(len(asgInfo.OriginalInstances)) {
+		state.logger.Infof("Ensuring ASG is in steady state (current capacity = desired capacity)")
+		err = waitForCapacity(asgSvc, eksAsgName, state.maxRetries, state.sleepBetweenRetries)
+		if err != nil {
+			state.logger.Error("Error waiting for ASG to reach steady state. Try again after the ASG is in a steady state.")
+			return err
+		}
+		state.logger.Infof("Verified ASG is in steady state (current capacity = desired capacity)")
+		asgInfo, err = getAsgInfo(asgSvc, eksAsgName)
+		if err != nil {
+			return err
+		}
+	}
+
+	state.GatherASGInfoDone = true
+	state.ASGs = append(state.ASGs, asgInfo)
+	return state.persist()
+}
+
+// ensureMaxRetries ensures we always have a proper value for maxRetries, either set by the end user
+// or calculated based on the original capacity
+func ensureMaxRetries(maxRetries int, sleepBetweenRetries time.Duration, originalCapacity int64) int {
+	logger := logging.GetProjectLogger()
+	// Calculate default max retries
+	if maxRetries == 0 {
+		defaultMaxRetries := getDefaultMaxRetries(originalCapacity, sleepBetweenRetries)
+		logger.Infof(
+			"No max retries set. Defaulted to %d based on sleep between retries duration of %s and scale up count %d.",
+			defaultMaxRetries,
+			sleepBetweenRetries,
+			originalCapacity,
+		)
+		return defaultMaxRetries
+	} else {
+		return maxRetries
+	}
+}
+
+// setMaxCapacity will set the max size of the auto scaling group.
+func (state *DeployState) setMaxCapacity(asgSvc *autoscaling.AutoScaling) error {
+	if state.SetMaxCapacityDone {
+		state.logger.Debug("Max capacity already set - skipping")
+		return nil
+	}
+	asg := &state.ASGs[0]
+	maxCapacityForUpdate := asg.OriginalCapacity * 2
+	if asg.OriginalMaxCapacity < maxCapacityForUpdate {
+		err := setAsgMaxSize(asgSvc, asg.Name, maxCapacityForUpdate)
+		if err != nil {
+			return err
+		}
+	}
+	asg.MaxCapacityForUpdate = maxCapacityForUpdate
+	state.SetMaxCapacityDone = true
+	return state.persist()
+}
+
+// scaleUp will scale up the ASG and wait until all the nodes are available.
+func (state *DeployState) scaleUp(asgSvc *autoscaling.AutoScaling) error {
+	if state.ScaleUpDone {
+		state.logger.Debug("Scale up already done - skipping")
+		return nil
+	}
+	asg := &state.ASGs[0]
+	state.logger.Info("Starting with the following list of instances in ASG:")
+	state.logger.Infof("%s", strings.Join(asg.OriginalInstances, ","))
+
+	state.logger.Infof("Launching new nodes with new launch config on ASG %s", asg.Name)
+	newInstanceIds, err := scaleUp(asgSvc, asg.Name, asg.OriginalInstances, asg.MaxCapacityForUpdate, state.maxRetries, state.sleepBetweenRetries)
+	if err != nil {
+		return err
+	}
+	state.logger.Infof("Successfully launched new nodes with new launch config on ASG %s", asg.Name)
+	state.ScaleUpDone = true
+	asg.NewInstances = newInstanceIds
+	return state.persist()
+}
+
+// waitForNodes will wait until all the new nodes are available. Specifically:
+// - Wait for the capacity in the ASG to meet the desired capacity (instances are launched)
+// - Wait for the new instances to be ready in Kubernetes
+// - Wait for the new instances to be registered with external load balancers
+func (state *DeployState) waitForNodes(ec2Svc *ec2.EC2, elbSvc *elb.ELB, elbv2Svc *elbv2.ELBV2, kubectlOptions *kubectl.KubectlOptions) error {
+	if state.WaitForNodesDone {
+		state.logger.Debug("Wait for nodes already done - skipping")
+		return nil
+	}
+	asg := &state.ASGs[0]
+	err := waitAndVerifyNewInstances(ec2Svc, elbSvc, elbv2Svc, asg.NewInstances, kubectlOptions, state.maxRetries, state.sleepBetweenRetries)
+	if err != nil {
+		state.logger.Errorf("Error while waiting for new nodes to be ready.")
+		state.logger.Errorf("Either resume with the recovery file or terminate the new instances.")
+		return err
+	}
+	state.logger.Infof("Successfully confirmed new nodes were launched with new launch config on ASG %s", asg.Name)
+	state.WaitForNodesDone = true
+	return state.persist()
+}
+
+// cordonNodes will cordon all the original nodes in the ASG so that Kubernetes won't schedule new Pods on them.
+func (state *DeployState) cordonNodes(ec2Svc *ec2.EC2, kubectlOptions *kubectl.KubectlOptions) error {
+	if state.CordonNodesDone {
+		state.logger.Debug("Nodes already cordoned - skipping")
+		return nil
+	}
+	asg := &state.ASGs[0]
+	state.logger.Infof("Cordoning old instances in cluster ASG %s to prevent Pod scheduling", asg.Name)
+	err := cordonNodesInAsg(ec2Svc, kubectlOptions, asg.OriginalInstances)
+	if err != nil {
+		state.logger.Errorf("Error while cordoning nodes.")
+		state.logger.Errorf("Either resume with the recovery file or continue to cordon nodes that failed manually, and then terminate the underlying instances to complete the rollout.")
+		return err
+	}
+	state.logger.Infof("Successfully cordoned old instances in cluster ASG %s", asg.Name)
+	state.CordonNodesDone = true
+	return state.persist()
+}
+
+// drainNodes drains all the original nodes in Kubernetes.
+func (state *DeployState) drainNodes(ec2Svc *ec2.EC2, kubectlOptions *kubectl.KubectlOptions, drainTimeout time.Duration, deleteLocalData bool) error {
+	if state.DrainNodesDone {
+		state.logger.Debug("Nodes already drained - skipping")
+		return nil
+	}
+	asg := &state.ASGs[0]
+	state.logger.Infof("Draining Pods on old instances in cluster ASG %s", asg.Name)
+	err := drainNodesInAsg(ec2Svc, kubectlOptions, asg.OriginalInstances, drainTimeout, deleteLocalData)
+	if err != nil {
+		state.logger.Errorf("Error while draining nodes.")
+		state.logger.Errorf("Either resume with the recovery file or continue to drain nodes that failed manually, and then terminate the underlying instances to complete the rollout.")
+		return err
+	}
+	state.logger.Infof("Successfully drained all scheduled Pods on old instances in cluster ASG %s", asg.Name)
+	state.DrainNodesDone = true
+	return state.persist()
+}
+
+// detachInstances detaches the original instances from the ASG and auto decrements the ASG desired capacity
+func (state *DeployState) detachInstances(asgSvc *autoscaling.AutoScaling) error {
+	if state.DetachInstancesDone {
+		state.logger.Debug("Instances already detached - skipping")
+		return nil
+	}
+	asg := &state.ASGs[0]
+	state.logger.Infof("Removing old nodes from ASG %s: %s", asg.Name, strings.Join(asg.OriginalInstances, ","))
+	err := detachInstances(asgSvc, asg.Name, asg.OriginalInstances)
+	if err != nil {
+		state.logger.Errorf("Error while detaching the old instances.")
+		state.logger.Errorf("Either resume with the recovery file or continue to detach the old instances and then terminate the underlying instances to complete the rollout.")
+		return err
+	}
+	state.DetachInstancesDone = true
+	return state.persist()
+}
+
+// terminateInstances terminates the original instances in the ASG.
+func (state *DeployState) terminateInstances(ec2Svc *ec2.EC2) error {
+	if state.TerminateInstancesDone {
+		state.logger.Debug("Instances already terminated - skipping")
+		return nil
+	}
+	asg := &state.ASGs[0]
+	state.logger.Infof("Terminating old nodes: %s", strings.Join(asg.OriginalInstances, ","))
+	err := terminateInstances(ec2Svc, asg.OriginalInstances)
+	if err != nil {
+		state.logger.Errorf("Error while terminating the old instances.")
+		state.logger.Errorf("Either resume with the recovery file or continue to terminate the underlying instances to complete the rollout.")
+		return err
+	}
+	state.logger.Infof("Successfully removed old nodes from ASG %s", asg.Name)
+	state.TerminateInstancesDone = true
+	return state.persist()
+}
+
+// restoreCapacity restores the max size of the ASG to its original value.
+func (state *DeployState) restoreCapacity(asgSvc *autoscaling.AutoScaling) error {
+	if state.RestoreCapacityDone {
+		state.logger.Debug("Capacity already restored - skipping")
+		return nil
+	}
+	asg := &state.ASGs[0]
+	err := setAsgMaxSize(asgSvc, asg.Name, asg.OriginalMaxCapacity)
+	if err != nil {
+		state.logger.Errorf("Error while restoring ASG %s max size to %v.", asg.Name, asg.OriginalMaxCapacity)
+		state.logger.Errorf("Either resume with the recovery file or adjust ASG max size manually to complete the rollout.")
+		return err
+	}
+	return state.persist()
+}
+
+// Retrieves current state of the ASG and returns the original Capacity and the IDs of the instances currently
+// associated with it.
+func getAsgInfo(asgSvc *autoscaling.AutoScaling, asgName string) (ASG, error) {
+	logger := logging.GetProjectLogger()
+	logger.Infof("Retrieving current ASG info")
+	asg, err := GetAsgByName(asgSvc, asgName)
+	if err != nil {
+		return ASG{}, err
+	}
+	originalCapacity := *asg.DesiredCapacity
+	maxSize := *asg.MaxSize
+	currentInstances := asg.Instances
+	currentInstanceIDs := idsFromAsgInstances(currentInstances)
+	logger.Infof("Successfully retrieved current ASG info.")
+	logger.Infof("\tCurrent desired capacity: %d", originalCapacity)
+	logger.Infof("\tCurrent max size: %d", maxSize)
+	logger.Infof("\tCurrent capacity: %d", len(currentInstances))
+	return ASG{
+		Name:                asgName,
+		OriginalCapacity:    originalCapacity,
+		OriginalMaxCapacity: maxSize,
+		OriginalInstances:   currentInstanceIDs,
+	}, nil
+}
diff --git a/eks/drain.go b/eks/drain.go
index 4f2c55d..a1fee49 100644
--- a/eks/drain.go
+++ b/eks/drain.go
@@ -41,7 +41,7 @@ func DrainASG(
 		if err != nil {
 			return err
 		}
-		allInstanceIDs = append(allInstanceIDs, asgInfo.currentInstanceIDs...)
+		allInstanceIDs = append(allInstanceIDs, asgInfo.OriginalInstances...)
 	}
 	logger.Infof("Found %d instances across all requested ASGs.", len(allInstanceIDs))
 


Test patch:
diff --git a/eks/deploy_state_test.go b/eks/deploy_state_test.go
new file mode 100644
index 0000000..2d4860f
--- /dev/null
+++ b/eks/deploy_state_test.go
@@ -0,0 +1,100 @@
+package eks
+
+import (
+	"github.com/gruntwork-io/kubergrunt/logging"
+	"github.com/stretchr/testify/assert"
+	"io/ioutil"
+	"net/url"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseNonExistingDeployState(t *testing.T) {
+	t.Parallel()
+	fileName := "./.na"
+	state, err := initDeployState(fileName, false, 3, 30*time.Second)
+	require.NoError(t, err)
+	defer os.Remove(fileName)
+
+	assert.Equal(t, fileName, state.Path)
+	assert.Equal(t, 3, state.maxRetries)
+	assert.Equal(t, 30*time.Second, state.sleepBetweenRetries)
+
+	assert.False(t, state.SetMaxCapacityDone)
+	assert.False(t, state.TerminateInstancesDone)
+	assert.False(t, state.GatherASGInfoDone)
+	assert.False(t, state.RestoreCapacityDone)
+	assert.False(t, state.DrainNodesDone)
+	assert.False(t, state.CordonNodesDone)
+	assert.False(t, state.DetachInstancesDone)
+	assert.False(t, state.WaitForNodesDone)
+	assert.False(t, state.ScaleUpDone)
+}
+
+func TestParseExistingDeployState(t *testing.T) {
+	t.Parallel()
+
+	stateFile := generateTempStateFile(t)
+	state, err := initDeployState(stateFile, false, 3, 30*time.Second)
+	require.NoError(t, err)
+	defer os.Remove(stateFile)
+
+	assert.True(t, state.GatherASGInfoDone)
+	assert.False(t, state.SetMaxCapacityDone)
+	assert.Equal(t, 1, len(state.ASGs))
+	assert.Equal(t, 3, state.maxRetries)
+	assert.Equal(t, 30*time.Second, state.sleepBetweenRetries)
+
+	asg := state.ASGs[0]
+
+	assert.Equal(t, "my-test-asg", asg.Name)
+	assert.Equal(t, int64(2), asg.OriginalCapacity)
+	assert.Equal(t, int64(4), asg.OriginalMaxCapacity)
+	assert.Equal(t, 2, len(asg.OriginalInstances))
+	assert.Equal(t, 1, len(asg.NewInstances))
+}
+
+func TestParseExistingDeployStateIgnoreCurrent(t *testing.T) {
+	t.Parallel()
+
+	stateFile := generateTempStateFile(t)
+	state, err := initDeployState(stateFile, true, 3, 30*time.Second)
+	require.NoError(t, err)
+	defer os.Remove(stateFile)
+
+	assert.False(t, state.GatherASGInfoDone)
+	assert.Equal(t, 0, len(state.ASGs))
+}
+
+func generateTempStateFile(t *testing.T) string {
+	escapedTestName := url.PathEscape(t.Name())
+	tmpfile, err := ioutil.TempFile("", escapedTestName)
+	require.NoError(t, err)
+	defer tmpfile.Close()
+
+	asg := ASG{
+		Name:                "my-test-asg",
+		OriginalCapacity:    2,
+		OriginalMaxCapacity: 4,
+		OriginalInstances: []string{
+			"instance-1",
+			"instance-2",
+		},
+		NewInstances: []string{
+			"instance-3",
+		},
+	}
+
+	state := &DeployState{
+		logger:            logging.GetProjectLogger(),
+		GatherASGInfoDone: true,
+		Path:              tmpfile.Name(),
+		ASGs:              []ASG{asg},
+	}
+
+	state.persist()
+	return tmpfile.Name()
+}