Okay, here are the questions, confusions, and requests for clarification regarding deployment strategies, grouped by topic, translated where necessary, and rephrased for a consistent style. They are ordered roughly by frequency, starting with the most common themes:

1. Database Migrations & Data Handling:

  • I'm confused about handling database schema changes (like adding/dropping columns, altering tables, changing relationships) with zero-downtime deployment strategies like Blue-Green, Canary, or Rolling Updates. How can the old version still work if the schema changes?
  • How do you ensure database backward compatibility, especially to allow for rollbacks? What tools or strategies (like Liquibase) can help?
  • When using strategies like Blue-Green or Canary with shared databases, how is data synchronized between versions or environments during the transition? What happens to data written by the new version if I need to roll back?
  • Specifically for Blue-Green, if the green database environment starts in read-only mode, how can I test application compatibility with new schema changes before the switchover?
  • What happens with stateful applications or long-running background jobs that depend on database state during these deployments?
  • Can you explain database migration strategies like Expand/Contract in more detail, particularly regarding potential write-locks or data conflicts during the process?

2. Strategy Differences & Clarifications (Blue-Green vs. Canary vs. Rolling, etc.):

  • What are the main differences between Blue-Green, Canary, Rolling Update, Recreate, Shadow, and A/B testing deployment strategies? They seem quite similar in some aspects.
  • I'm particularly confused about the difference between Canary and Rolling Update, and between Blue-Green and Canary. Isn't Canary just a slower Rolling Update or a form of A/B testing?
  • Some demos seem to mix concepts (e.g., showing user-specific routing in what's called Blue-Green). Can you clarify the defining characteristics, especially regarding traffic switching (all at once vs. gradual/partial)?
  • Is using feature flags/toggles a distinct deployment strategy, or is it a technique used alongside others like Blue-Green? How does it compare?
  • What exactly is a Shadow deployment? Why wasn't it covered?
  • What does "Recreate" mean compared to Blue-Green?

3. Infrastructure Setup, Cost & Networking:

  • How is the infrastructure actually set up for strategies like Blue-Green? Do I need fully duplicate environments (VMs, clusters)? Isn't that expensive due to doubling infrastructure costs?
  • Can Blue-Green be achieved within a single cluster using namespaces instead of needing entirely separate clusters?
  • How is traffic actually switched in Blue-Green? Is using DNS reliable given caching issues? How does the load balancer handle the switch? Do I need multiple IPs or load balancers?
  • For Canary, how is the infrastructure set up if we're not creating a whole new environment? Are we just deploying the new version to a subset of existing servers?
  • How does Blue-Green work specifically for serverless functions like AWS Lambda where there isn't a traditional load balancer or persistent server fleet?
  • How does server segregation work during deployment (assigning specific servers to blue vs. green)?
  • What does the term 'warm' fleet mean in the context of preparing servers for deployment?
  • How are cloud recommendations (like minor DB engine or OS updates) handled during a major Blue-Green RDS upgrade? Do they need to be done first or are they handled automatically?

4. Tooling, Automation & Implementation Details:

  • How are these strategies, like Canary or Blue-Green, actually implemented in Kubernetes? Is it just kubectl rollout or does it require more complex tooling like Istio, Flagger, Argo Rollouts, Helm, Nginx Ingress, Traefik, Kong, etc.?
  • Can you provide practical examples or demos using specific tools like Jenkins, Helm, Istio, Flagger, Argo Rollouts, or cloud provider services (AWS CodeDeploy, Azure DevOps pipelines, App Engine) to automate these strategies?
  • How do tools like Argo Rollouts (replacing Deployment with Rollout) compare to Flagger (referencing existing Deployment) in practice, especially when dealing with third-party Helm charts?
  • How can I manage different Kube config maps (e.g., for feature flags) across preview/active services when using tools like Argo Rollouts?
  • Can you explain specific configurations in tools, like appspec.yml TaskDefinition ARN versioning in AWS ECS deployments or spec.strategy.canary.analysis.args in Argo Rollouts?
  • Is it possible to automate the service switch/label change in Blue-Green deployments via commands or operators instead of manual changes?
  • How does Jenkins add benefit to an AWS CodeDeploy pipeline if the outcome seems achievable without it?
  • How do I apply these strategies when dealing with multiple interconnected microservices, especially internal ones not directly exposed via Ingress? How does service A's canary talk to service B's canary without Istio?

5. Rollback & Failure Handling:

  • How does rollback actually work, especially in automated pipelines? If a deployment (e.g., green environment, canary percentage) fails validation or health checks, how is the traffic automatically reverted?
  • What happens to the YAML configuration file image version if a rollback occurs using kubectl rollout undo? How do you track changes across revisions, especially after rollbacks?
  • How do you handle rollbacks when database schema changes have already been applied?
  • What happens if a deployment is paused, a hotfix image is pushed, and then the deployment is resumed?

6. Request & Session Handling during Transitions:

  • What happens to in-flight user requests when traffic is switched (e.g., from Blue to Green, or during a Rolling Update)? Do users experience failures or errors?
  • How are existing connections drained gracefully from the old version before it's scaled down? How long does this take?
  • How are user sessions handled during a switchover? Do they need to be moved?
  • How can I ensure zero downtime during the swap/switchover, especially under high load?

7. Applicability & Use Cases:

  • Does Blue-Green make sense for a first-time deployment (Day 0)?
  • Are strategies like Blue-Green suitable for stateful applications?
  • How would you apply these strategies to applications using specific technologies like Tomcat, JBoss, Kafka consumers, or multi-container pods?
  • Which strategy is generally preferred or most used in real-time production environments? Which should I mention in an interview?
  • Can progressive delivery be used based on region or timezone?
  • Can these strategies be applied to upgrading infrastructure components or third-party apps (like ingress controllers, cert-manager, Prometheus)?

8. Testing & Validation:

  • How are deployments validated in the "green" environment before switching traffic in Blue-Green? What kind of tests (smoke, performance, functional) are typically run?
  • How is analysis performed in Canary deployments, especially with low/no traffic or when changes affect only specific endpoints? Can you show examples using web analysis or metrics?
  • How can QA teams test a canary deployment in production if only a small percentage of traffic is routed, and how can they specifically target the new version?
  • Can a Blue-Green deployment switch be triggered automatically based on successful smoke tests?

9. General Confusion & Basic Clarifications:

  • I'm finding the patterns confusing as they seem similar; could you clearly highlight the core differences again?
  • What does the term 'rollout' mean in Kubernetes? Is it just moving to the next version?
  • What is the difference between kubectl patch deployment and using a Rolling Update strategy?
  • What's the difference between a Kubernetes Deployment and a ReplicaSet in the context of updates?
  • How can we have different code versions running if the code is developed in one place? (Fundamental confusion about deployment artifacts).
  • Is achieving true zero downtime actually possible?