Refer to the exhibit. A DevOps engineer is deploying a stack of services with Docker Compose. A containerized application running in the app Docker container must communicate with the web-server Docker container running a NGINX web server. How must communication between the two Docker containers be configured?

```yaml
version: "3.3"
services:
app:
build: .
environment:
SERVER_NAME: web-server
depends_on:
- web-server
web-server:
image: nginx
```

Question

Refer to the exhibit. A DevOps engineer is deploying a stack of services with Docker Compose. A containerized application running in the app Docker container must communicate with the web-server Docker container running a NGINX web server. How must communication between the two Docker containers be configured?

```yaml
version: "3.3"
services:
 app:
 build: .
 environment:
 SERVER_NAME: web-server
 depends_on:
 - web-server
 web-server:
 image: nginx
```

Accepted Answer

C. The application running in the app Docker container will use DNS to resolve the SERVER_NAME environment variable that contains web-server to an IP address. When Docker Compose creates services, it also sets up a default network for these services. Within this network, each service name (like 'web-server') acts as a hostname that can be resolved by other containers in the same network through Docker's embedded DNS service. Therefore, the application in the 'app' container can use the value 'web-server' from the 'SERVER_NAME' environment variable to look up the IP address of the 'web-server' container via DNS and establish communication.

Answer

A. Docker containers are completely isolated from each other, so the two Docker containers will not communicate with each other. Docker containers within the same Docker Compose network are explicitly designed to communicate with each other, contradicting the statement that they are completely isolated and cannot communicate.

Answer

B. Docker Compose will use the depends_on configuration to provide the app Docker container with the IP address of the web-server Docker container. The 'depends_on' configuration in Docker Compose only ensures that 'web-server' is started before 'app'; it does not inject IP addresses directly into environment variables or handle network resolution for the application.

Answer

D. The application running in the app Docker container will use ARP to resolve the SERVER_NAME environment variable that contains web-server to an IP address. ARP (Address Resolution Protocol) maps IP addresses to MAC addresses within a local network segment, which is a lower-level network protocol and not how applications within Docker containers typically resolve service names to IP addresses for inter-container communication.

Refer to the exhibit. A DevOps engineer is deploying a stack of services with Docker Compose. A containerized application running in the app Docker container must communicate with the web-server Docke

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