Top AWS OpsWorks Stacks Interview Questions and Answers

Introduction

AWS OpsWorks Stacks is a digital handyman for managing your apps and servers on Amazon's cloud. It helps you set up and run your software smoothly without doing everything manually. You can think of it as your assistant for handling tasks like launching new servers, updating apps, and scaling resources automatically based on demand. For experienced pros, knowing how to use OpsWorks Stacks is a big plus in AWS job interviews. It shows you can handle complex tasks efficiently, making it easier to manage your projects and impress potential employers.

Q1: What Are AWS OpsWorks Stacks?

A: AWS OpsWorks Stacks is the only service that performs configuration management tasks. Configuration management is the process designed to ensure that the infrastructure in a given system adheres to a specific set of standards, settings, or attributes (its configuration). Popular configuration management tools include Chef and Puppet. AWS OpsWorks Stacks allows you to manage the configuration of both on-premises and cloud infrastructures. To accomplish this, you organize units of infrastructure into stacks and layers.

Q2: What Is The Role Of Stack Name?

A: Stack Name identifies stacks in the AWS OpsWorks Stacks console. Since this name is not unique, AWS OpsWorks assigns a Globally Unique Identifier (GUID) to the stack after you create it.

Q3: What Is Amazon Elastic Container Service?

A: Amazon Elastic Container Service (Amazon ECS) allows you to define the requirements of, schedule, and configure Docker containers to deploy to a cluster of Amazon EC2 instances. The cluster itself can be quickly provisioned with AWS CloudFormation and configuration of container requirements such as CPU and memory needs. Combining this with configuration management tools allows the cluster and any active containers to be configured dynamically.

Q4: How Does Amazon ECS Cluster Layer work?

A: Amazon ECS cluster layers provide configuration management capabilities to Linux instances in your Amazon ECS cluster. You can associate a single cluster with a single stack at a time. To create this layer, you must register the cluster with the stack. After this, it will appear in the Layer type drop-down list of available clusters to create a layer.

Q5: What Are Target Tracking Policies?

A: Target tracking policies determine when to scale the number of tasks based on a target metric. If the metric is above the target, such as CPU utilization is above 75 percent, Amazon ECS can automatically launch more tasks to bring the metric below the desired value. You can specify multiple target tracking policies for the same service. In the case of a conflict, the policy that would result in the highest task count wins.

Q6: What Is Amazon ECS Cluster?

A: Amazon ECS clusters are the foundational infrastructure components on which containers run. Clusters consist of one or more Amazon EC2 instances in your Amazon VPC. Each Instance in a cluster (cluster instance) has an agent installed. The agent is responsible for receiving container scheduling/shutdown commands from the Amazon ECS service and reporting the current health status of containers (restart or replace).

Q7: What Is The API Endpoint Region?

A: AWS OpsWorks associates a stack with either a global endpoint or one of multiple regional endpoints. When you create a resource in the stack, such as an instance, it is available only from the endpoint you specify when you create the stack. For example, suppose a stack is created with the global "classic" endpoint. In that case, any instances will be accessible only by AWS OpsWorks Stacks that use the global API endpoint in the US East (N. Virginia) region. Resources are not available across regional endpoints.

Q8: How To Enable Auto-Healing Instances?

A: If you enable auto healing for a layer, instances that fail to communicate with the AWS OpsWorks service endpoint for more than 5 minutes restart automatically. You can view this in the Amazon CloudWatch Events console, where initiated_by is set to auto-healing. Auto-healing is enabled by default on all layers in a stack, but you can disable them at any time.

When instances are auto-healed, the exact behavior depends on the type of Instance.

• For Instance, the underlying Instance terminates in store-backed instances, and a new one is created in its place.

• Amazon EBS-backed instances stop and start with the appropriate Amazon EC2 API command.

Q9: What Is The Role Of Amazon ECS Container Agent?

A: The Amazon ECS container agent monitors the status of tasks that run on cluster instances. If a new task needs to be launched, the container agent downloads the container images and starts or stops containers. If any containers fail health checks, the container agent replaces them. Since the AWS Fargate launch type uses AWS-managed compute resources, you do not need to configure the agent.

To register an instance with an Amazon ECS cluster, you must first install the Amazon ECS Agent. This agent installs automatically on Amazon ECS-optimized AMIs. If you would like to use a custom AMI, it must adhere to the following requirements:

• Linux kernel 3.10 or greater

• Docker version 1.9.0 or greater and any corresponding dependencies

Q10: What Are The Different Types of Built-In Layers AWS OpsWorks Stack Provides?

A: AWS OpsWorks Stacks provides several built-in layers for Chef 11.10 stacks.

• HAProxy layer

• MySQL layer

• AWS Flow (Ruby) layer

• Java app server layer

• Node.js app server layer

• PHP app server layer

• Rails layer

• Static web server layer

• Amazon ECS cluster layer

Q11: What Is The Role Of Layer In Stack?

A: A layer acts as a subset of instances or resources in a stack. Layers act as groups of instances or resources based on a standard function. This is especially important, as the Chef recipe code applies to a layer and all instances in a layer. A layer is where any configuration of nodes will be set, such as what Chef recipes to execute at each lifecycle hook. A layer can contain any or more nodes, and a node must be a member of one or more layers. When a node is a member of multiple layers, it will run any recipes you configure for each lifecycle event for both layers in the layer and recipe order you Specify. 

From the point of view of a Chef Server installation, a layer is synonymous with a Chef Role. In the node object, the layer and role data are equivalent. This primarily ensures compatibility with open-source cookbooks not explicitly written for AWS OpsWorks Stacks.

Q12: How Does The Amazon RDS Layer Work?

A: Amazon RDS layers pass connection information to an existing Amazon RDS instance. When you associate an Amazon RDS instance to a stack, it is assigned to an app. This passes the connection information to the instances via the app's deploy attributes, and you can access the data within your Chef recipes with node[: deploy][:app_name][:database] hash.

You can associate a single Amazon RDS instance with multiple apps in the same stack. However, you cannot associate multiple Amazon RDS instances with the same app. If your application needs to connect multiple databases, use custom JSON to include the connection information for the other database(s).

Q13: What Are Blue/Green Deployments (Separate Stacks)?

A: Just as you use separate stacks for different environments of the same application, you can also use separate stacks for different deployments. This ensures that all application features and updates can be thoroughly tested before routing requests to the new environment. Additionally, you can leave the previous environment running for some time to perform backups, investigate logs, or perform other tasks.

When you use Elastic Load Balancing layers and Amazon Route 53, you can route traffic to the new environment with built-in weighted routing policies. You can progressively increase traffic to the new stack as health checks and other monitoring indicate the new application version has deployed without error.

Q14: What Are The Different Instance Types AWS OpsStacks Supports?

A: AWS OpsWorks Stacks supports three instance types.

• 24/7 instances- This instance type runs until you manually stop it. 

• Time-based instances- Instances of this type run on a daily and weekly schedule that you configure and help handle predictable changes in a load on your stack.

• Load-based instances- Load-based instances start and stop automatically based on metrics such as NetworkOut or CPU utilization.

You can use time-based and load-based instances to implement automatic scaling in response to predictable or sudden changes in demand. However, unlike Amazon EC2 Auto Scaling groups, you must create time-based and load-based instances ahead of time with the AWS OpsWorks console or AWS CLI. The underlying Amazon EC2 instance will not be created until the time you specify or the load threshold occurs, but the AWS OpsWorks instance object must exist ahead of time.

Q15: How Do You Update The Instance?

A: When an instance first boots, AWS OpsWorks Stacks will automatically install any new security and package updates. However, after the initial boot, this will not occur again. This is to ensure that future updates do not affect the performance of your applications. For Linux stacks, you can initiate updates with the Update Dependencies command. Windows stacks do not provide any built-in means to perform updates.

Alternatively, to update instances directly, you can regularly launch new instances to replace old ones. As the new instances are created, they will be patched with the latest available security and operating system updates. If you want to prevent updates entirely and manage this through a separate process, instances can be set not to install updates on startup when you create them. Additionally, this can be set at the layer level to propagate to any new instances you add.

Q16: How Can You Register Instances?

A: If instances are running in your data center or other Amazon EC2 instances in your account (or even other accounts), you can register those instances with your stack. You can perform tasks such as user management, package updates, operating system upgrades, and application deployments on registered instances in the same manner as "native" instances.

You use the aws opsworks register AWS CLI command to register an instance with a stack. The command will install the AWS OpsWorks agent on the Instance, responsible for communicating with the AWS OpsWorks Stacks service endpoint to receive commands and publish information. When you register with other Amazon EC2 instances, they will need both an AWS Identity and Access Management (IAM) instance profile or IAM user credentials with access to register instances with the AWS CLI via the AWS managed policy, AWSOpsWorksRegisterWithCLI.

When you register instances, you must provide a valid SSH user and private key or valid username and password. These must correspond to a Linux user on the target system (unless you call the register command from the target system itself). After the Instance registers, it will display in the AWS OpsWorks Stacks console for assignment to one or more layers in your stack.

Q17: What Are The Different Permission Types To Provide Stack-Level Permission?

A: You can apply four permission types to a user to provide stack-level permission.

• Deny- No action is allowed on the stack.

• Show- The user can view stack configuration but cannot interact with it in any way.

• Deploy- The user can view stack configuration and deploy apps.

• Manage- The user can view stack configuration, deploy apps, and manage stack configuration.

AWS OpsWorks Stacks permissions do not allow specific actions, such as creating or cloning stacks. IAM permissions restrict these actions, and you must assign them to an IAM user or IAM role. You can fine-tune the permissions levels if the user in question is also an IAM user.

Along with stack-level permissions, you can give AWS OpsWorks users SSH or RDP access into instances with or without administrative access. You can also configure users to manage their own SSH keys so that they can set their key once they provide access and do not require shared critical files through other means. This is also more secure than Amazon EC2 key pairs, as the keys are unique to individual users.

Q18: How Do You Manage Databases Between Deployment?

A: In either deployment strategy, there will likely be a backend database with which instances running either version must be communicated. Currently, Amazon RDS layers support registering a database with only one stack at a time.

Suppose you want to avoid creating a new database and migrating data as part of the deployment process. In that case, you can configure both application version instances to connect to the same database (if there are no schema changes that would prevent this). Whichever stack does not have the Amazon RDS instance registered will need to obtain credentials via another means, such as custom JSON or a configuration file in a secure Amazon S3 bucket.

If schema changes are not backward compatible, create a new database to provide the most seamless transition. However, it will be essential to preserve data during the transition process. You should test this heavily before you attempt it during a production deployment.

Q19: What Is The Role Of AWS Fargate?

A: AWS Fargate simplifies managing containers in your environment and removes the need to manage underlying cluster instances. Instead, you only need to specify the compute requirements of your containers in your task definition. AWS Fargate automatically launches containers without your interaction.

With AWS Fargate, there are several restrictions on the types of tasks that you can launch. For example, when you specify a task definition, containers cannot be run in privileged mode. To verify that a given task definition is acceptable by AWS Fargate, use the Requires capabilities field of the Amazon ECS console or the --requires-capabilities command option of the AWS CLI.

Q20: How Do Task Placement Strategies Work?

A: Regardless of your method, task placement strategies determine which instances tasks launch or terminate during scaling actions. For example, the spread task placement strategy distributes tasks across multiple AZs as much as possible. Task placement strategies are performed on a best-effort basis. If the strategy cannot be honored, such as when there are insufficient compute resources in the AZ you select, Amazon ECS will still try to launch the task(s) on other cluster instances. Other strategies include binpack (uses CPU and memory on each Instance at a time) and random.

Task placement strategies are associated with specific attributes evaluated during task placement. For example, to spread tasks across availability zones, the placement strategy to use is as follows:

Conclusion

JanBask Training's AWS courses can significantly aid in mastering AWS OpsWorks Stacks and other essential AWS services. These courses offer comprehensive, easy-to-follow training modules to equip learners with the skills needed to excel in AWS environments. By enrolling in JanBask's AWS courses, individuals can gain hands-on experience with OpsWorks Stacks, learning how to efficiently manage applications and infrastructure through practical exercises and real-world scenarios.