🧾 Docker Directory Change, EBS Setup & Custom Networking

---

✅ PART 1 – Attach and Mount a New EBS Volume to EC2

📌 Goal:

Avoid root volume exceeding 50% usage by moving Docker data to a new EBS volume.

🔧 Steps:

1. Create a New EBS Volume

   • Must be in same region and AZ as the EC2 instance.

   • Attach it to the EC2 instance (e.g., as /dev/xvdf).

2. Check the Volume for Filesystem

    sudo file -s /dev/xvdf
   

   • If it shows data, it has no filesystem yet.

3. Format the Volume

    sudo mkfs.ext4 /dev/xvdf
   

4. Get UUID

    sudo lsblk -o +UUID
   

   • Example UUID: 5a8bd636-5809-47fa-927c-027de4350f0c

5. Create Mount Directory

    sudo mkdir /dockerData
   

6. Mount Permanently via /etc/fstab

    sudo nano /etc/fstab
   

   Add this line:

    UUID=5a8bd636-5809-47fa-927c-027de4350f0c  /dockerData  ext4  defaults,nofail  0  2
   

7. Mount Immediately (optional)

    sudo mount -a
   

---

✅ PART 2 – Change Docker's Default Data Directory

📌 Goal:

Move Docker storage to the new volume mounted at /dockerData.

🔧 Steps:

1. Check Current Docker Root Directory

    docker info | grep 'Docker Root Dir'
   

2. Edit Docker Service File

    sudo nano /lib/systemd/system/docker.service
   

   Replace the ExecStart line:

    ExecStart=/usr/bin/dockerd --data-root /dockerData -H fd:// --containerd=/run/containerd/containerd.sock
   

   🔁 This replaces the default root /var/lib/docker.

3. Reload and Restart Docker

    sudo systemctl daemon-reexec
    sudo systemctl daemon-reload
    sudo systemctl restart docker
   

4. Verify

    docker info | grep 'Docker Root Dir'
   

   Should show:

    Docker Root Dir: /dockerData
   

---

✅ PART 3 – Create and Use a Custom Docker Network

📌 Why?

• Containers are stateless and may change IPs after restart.

• Default bridge network does not allow container name resolution.

• When we say "the default bridge network does not allow container name resolution", we mean that:

  Containers connected to the default bridge network cannot communicate using each other’s container names (like ping app1). They must use IP addresses instead.

🔧 Setup:

1. Create a Custom Network

    docker network create custom --driver bridge
   

2. Verify

    docker network ls
   

3. Run Containers in Bridge (non-custom) – Names don't resolve

    docker run --rm -d --name app1 -p 8000:80 nginx:latest
    docker run --rm -d --name app2 -p 8001:80 nginx:latest
   

    docker exec -it app1 bash
    apt update && apt install iputils-ping
    ping <app2 IP> ✅
    ping app2 ❌ (fails in default bridge)
   

4. Run Containers in Custom Network – Name resolution works

    docker run --rm -d --name app3 -p 8003:80 --network custom nginx:latest
    docker run --rm -d --name app4 -p 8004:80 --network custom nginx:latest
   

   Inside app3 container:

    ping app4 ✅ (name-based ping works)
   

5. Add Existing Container to Custom Network

    docker network connect custom app1
    docker inspect custom
   

---

✅ Summary