Added day 37 tasks

Author: LondheShubham153

2026/day-37/README.md

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+# Day 37 – Docker Revision & Cheat Sheet
+
+## Goal
+Take a **one-day pause** to consolidate everything from Days 29–36 so Docker actually sticks.
+
+## Expected Output
+- A markdown file: `docker-cheatsheet.md`
+- A markdown file: `day-37-revision.md` with self-check answers
+
+---
+
+## Self-Assessment Checklist
+Mark yourself honestly — **can do**, **shaky**, or **haven't done**:
+
+- [ ] Run a container from Docker Hub (interactive + detached)
+- [ ] List, stop, remove containers and images
+- [ ] Explain image layers and how caching works
+- [ ] Write a Dockerfile from scratch with FROM, RUN, COPY, WORKDIR, CMD
+- [ ] Explain CMD vs ENTRYPOINT
+- [ ] Build and tag a custom image
+- [ ] Create and use named volumes
+- [ ] Use bind mounts
+- [ ] Create custom networks and connect containers
+- [ ] Write a docker-compose.yml for a multi-container app
+- [ ] Use environment variables and .env files in Compose
+- [ ] Write a multi-stage Dockerfile
+- [ ] Push an image to Docker Hub
+- [ ] Use healthchecks and depends_on
+
+---
+
+## Quick-Fire Questions
+Answer from memory, then verify:
+1. What is the difference between an image and a container?
+2. What happens to data inside a container when you remove it?
+3. How do two containers on the same custom network communicate?
+4. What does `docker compose down -v` do differently from `docker compose down`?
+5. Why are multi-stage builds useful?
+6. What is the difference between `COPY` and `ADD`?
+7. What does `-p 8080:80` mean?
+8. How do you check how much disk space Docker is using?
+
+---
+
+## Build Your Docker Cheat Sheet
+Create `docker-cheatsheet.md` organized by category:
+- **Container commands** — run, ps, stop, rm, exec, logs
+- **Image commands** — build, pull, push, tag, ls, rm
+- **Volume commands** — create, ls, inspect, rm
+- **Network commands** — create, ls, inspect, connect
+- **Compose commands** — up, down, ps, logs, build
+- **Cleanup commands** — prune, system df
+- **Dockerfile instructions** — FROM, RUN, COPY, WORKDIR, EXPOSE, CMD, ENTRYPOINT
+
+Keep it short — one line per command, something you'd actually reference on the job.
+
+---
+
+## Revisit Weak Spots
+Pick **2 topics** you marked as shaky and redo the hands-on tasks from that day.
+
+---
+
+## Suggested Flow (45–60 minutes)
+- 10 min: go through the checklist honestly
+- 10 min: answer quick-fire questions
+- 20 min: build your cheat sheet
+- 10 min: redo one weak area
+
+---
+
+## Submission
+1. Add `docker-cheatsheet.md` and `day-37-revision.md` to `2026/day-37/`
+2. Commit and push to your fork
+
+---
+
+## Learn in Public
+Share your Docker cheat sheet on LinkedIn — help others revise too.
+
+`#90DaysOfDevOps` `#DevOpsKaJosh` `#TrainWithShubham`
+
+Happy Learning!
+**TrainWithShubham**