Docker Certified Associate Exam Questions

: = Keeping a backup copy of the image on another repository is not how a user can prevent an image, such as 'nginx:latest', from being overwritten by another user with push access to the repository. This approach does not prevent the original image from being overwritten, it only provides a way to restore it from another source. However, this may not be reliable or efficient, as the backup repository may not be in sync with the original one, or may not be accessible at all times.To prevent an image from being overwritten by another user, the user can use the DTR web UI to make the tag immutable1. This feature allows the user to lock a specific tag, so that no one can push a new image with the same tag to the repository.This ensures that the image is always consistent and secure1.Reference:

Make a tag immutable | Docker Docs

: Tagging the image with 'nginx:immutable' isnothow a user can prevent an image, such as 'nginx:latest', from being overwritten by another user with push access to the repository. Tagging the image with 'nginx:immutable' will only create a new tag for the image, but it will not prevent the original tag from being overwritten.To prevent an image tag from being overwritten in Docker Trusted Registry, the user can use the DTR web UI to make the tag immutable1.This will prevent anyone from pushing a new image with the same tag, even if they have push access to the repository1.Alternatively, the user can also use the DTR API to make the tag immutable2.Reference:Prevent tags from being overwritten), DTR API reference)

= This is not a way to configure the Docker engine to use a registry without a trusted TLS certificate. There is no such option as IGNORE_TLS in the daemon.json configuration file.The daemon.json file is used to configure various aspects of the Docker engine, such as logging, storage, networking, and security1.To use a registry without a trusted TLS certificate, you need to either add the certificate to the trusted root certificates of the system, or configure the Docker engine to allow insecure registries2.To add the certificate to the trusted root certificates, you need to copy the certificate file to the /etc/docker/certs.d/<registry-hostname>/ directory on every Docker host2.To configure the Docker engine to allow insecure registries, you need to add the registry hostname or IP address to the ''insecure-registries'' array in the daemon.json file3. For example:

{ ''insecure-registries'' : [''myregistry.example.com:5000''] }

Note that using insecure registries is not recommended, as it exposes you to potential man-in-the-middle attacks and data corruption3.You should always use a registry with a trusted TLS certificate, or use Docker Content Trust to sign and verify your images4.Reference:

Daemon configuration file | Docker Docs

Verify repository client with certificates | Docker Docs

Test an insecure registry | Docker Docs

Content trust in Docker | Docker Docs

To trust a self-signed certificate from a Docker Trusted Registry (DTR), you need to place the certificate in the appropriate location on all cluster nodes and restart the Docker daemon. There are two possible locations for the certificate, depending on your OS and Docker version1:

* /etc/docker/certs.d/dtr.example.com/ca.crt: This is the preferred location for Linux systems and Docker versions 1.13 and higher. This directory is scanned by Docker for certificates and keys for each registry domain2.

* Your OS certificate path: This is the fallback location for other OSes and Docker versions. You need to find the certificate store for your OS and copy the certificate there. You also need to trust the certificate system-wide, which may require additional steps depending on your OS3.

The other options are not correct because:

* Passing '-trust-certificate ca.crt to the Docker client is not a valid option. There is no such flag for the Docker client4.

* Placing the certificate in '/etc/docker/dtr/dtr.example.com.crt' is not a valid location. The certificate should be in the /etc/docker/certs.d directory, not the /etc/docker/dtr directory1.

* Passing -- insecure-registry to the Docker client is not a recommended option. This flag disables the TLS verification for the registry, which makes the communication insecure and vulnerable to attacks.

* Use self-signed certificates | Docker Docs

* Test an insecure registry | Docker Docs

* Add TLS certificates as a trusted root authority to the host OS | Docker Docs

* docker | Docker Docs

* [Deploy a registry server | Docker Docs]

The --privileged flag lifts all the cgroup limitations for a container, as well as other security restrictions imposed by the Docker daemon1. This gives the container full access to the host's devices, resources, and capabilities, as if it was running directly on the host2. This can be useful for certain use cases that require elevated privileges, such as running Docker-in-Docker or debugging system issues3. However, using the --privileged flag also poses a security risk, as it exposes the host to potential attacks or damages from the container4. Therefore, it is not recommended to use the --privileged flag unless absolutely necessary, and only with trusted images and containers.

The other options are not correct because they do not lift all the cgroup limitations for a container, but only affect specific aspects of the container's resource allocation or isolation:

* The --cpu-period flag sets the CPU CFS (Completely Fair Scheduler) period for a container, which is the length of a CPU cycle in microseconds. This flag can be used in conjunction with the --cpu-quota flag to limit the CPU time allocated to a container. However, this flag does not affect other cgroup limitations, such as memory, disk, or network.

* The --isolation flag sets the isolation technology for a container, which is the mechanism that separates the container from the host or other containers. This flag is only available on Windows containers, and can be used to choose between process, hyperv, or process-isolated modes. However, this flag does not affect the cgroup limitations for a container, but only the level of isolation from the host or other containers.

* The --cap-drop flag drops one or more Linux capabilities for a container, which are the privileges that a process can use to perform certain actions on the system. This flag can be used to reduce the attack surface of a container by removing unnecessary or dangerous capabilities. However, this flag does not affect the cgroup limitations for a container, but only the capabilities granted to the container by the Docker daemon.

* Runtime privilege and Linux capabilities

* Docker Security: Using Containers Safely in Production

* Docker run reference

* Docker Security: Are Your Containers Tightly Secured to the Ship? SlideShare

* [Secure Engine]

* [Configure a Pod to Use a Limited Amount of CPU]

* [Limit a container's resources]

* [Managing Container Resources]

* [Isolation modes]

* [Windows Container Isolation Modes]

* [Windows Container Version Compatibility]

* [Docker and Linux Containers]

* [Docker Security Cheat Sheet]

* [Docker Security: Using Containers Safely in Production]