DCA Exam Dumps : Docker Certified Associate (DCA) Exam

The statement is correct. In the provided Docker Compose file, a health check is defined for the service “app”. It uses curl to perform a health check on the application every 10 seconds (as specified by the “interval” parameter). If it fails three times (as specified by the “retries” parameter), then the container is marked as unhealthy. A health check is a way of checking the health of a running container and applying actions based on the result1. It can be used to monitor the status of the service and restart the container if it becomes unhealthy2. References:

Compose file version 3 reference | Docker Docs

Docker Compose & Health Checks – Gabriel’s World

 Docker Content Trust (DCT) is a feature that allows users to verify the integrity and publisher of container images they pull or deploy from a registry server, signed on a Notary server12. DCT does not verify or encrypt the Docker registry TLS, which is a separate mechanism for securing the communication between the Docker client and the registry server. The purpose of DCT is to ensure that the images are not tampered with or maliciously modified by anyone other than the original publisher3. References:

Content trust in Docker | Docker Docs

Docker Content Trust: What It Is and How It Secures Container Images

Automation with content trust | Docker Docs

 The command docker service create -name dns-cache -p 53:53 -service udp dns-cache is not valid because it has some syntax errors. The correct syntax for creating a swarm service is docker service create [OPTIONS] IMAGE [COMMAND] [ARG...]. The errors in the command are:

There should be a space between the option flag and the option value. For example, -name dns-cache should be -name dns-cache.

The option flag for specifying the service mode is -mode, not -service. For example, -service udp should be -mode udp.

The option flag for specifying the port mapping is --publish or -p, not -p. For example, -p 53:53 should be --publish 53:53.

The correct command for creating a swarm service that only listens on port 53 using the UDP protocol is:

docker service create --name dns-cache --publish 53:53/udp dns-cache

This command will create a service called dns-cache that uses the dns-cache image and exposes port 53 on both the host and the container using the UDP protocol.

[docker service create | Docker Documentation] : [Publish ports for services | Docker Documentation]