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Developer-Guide.md

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Warning

This document is written specifically for developers: it is not intended for end users.

Assumptions

  • You are working on a non-critical test or development system.

Initial setup

The recommended way to create a development environment is to first install the packaged versions of the Kata Containers components to create a working system.

The installation guide instructions will install all required Kata Containers components, plus Docker*, the hypervisor, and the Kata Containers image and guest kernel.

Requirements to build individual components

You need to install the following to build Kata Containers components:

  • golang

    To view the versions of go known to work, see the golang entry in the versions database.

  • make.

  • gcc (required for building the shim and runtime).

Build and install the Kata Containers runtime

$ go get -d -u github.com/kata-containers/runtime
$ cd $GOPATH/src/github.com/kata-containers/runtime
$ make && sudo -E PATH=$PATH make install

The build will create the following:

  • runtime binary: /usr/local/bin/kata-runtime
  • configuration file: /usr/share/defaults/kata-containers/configuration.toml

Check hardware requirements

You can check if your system is capable of creating a Kata Container by running the following:

$ sudo kata-runtime kata-check

If your system is not able to run Kata Containers, the previous command will error out and explain why.

Configure to use initrd or rootfs image

Kata containers can run with either an initrd image or a rootfs image.

If you want to test with initrd, make sure you have initrd = /usr/share/kata-containers/kata-containers-initrd.img in your configuration file, commenting out the image line:

/usr/share/defaults/kata-containers/configuration.toml and comment out the image line with the following. For example:

$ sudo mkdir -p /etc/kata-containers/
$ sudo install -o root -g root -m 0640 /usr/share/defaults/kata-containers/configuration.toml /etc/kata-containers
$ sudo sed -i 's/^\(image =.*\)/# \1/g' /etc/kata-containers/configuration.toml

You can create the initrd image as shown in the create an initrd image section.

If you want to test with a rootfs image, make sure you have image = /usr/share/kata-containers/kata-containers.img in your configuration file, commenting out the initrd line. For example:

$ sudo mkdir -p /etc/kata-containers/
$ sudo install -o root -g root -m 0640 /usr/share/defaults/kata-containers/configuration.toml /etc/kata-containers
$ sudo sed -i 's/^\(initrd =.*\)/# \1/g' /etc/kata-containers/configuration.toml

The rootfs image is created as shown in the create a rootfs image section.

One of the initrd and image options in Kata runtime config file MUST be set but not both. The main difference between the options is that the size of initrd(10MB+) is significantly smaller than rootfs image(100MB+).

Enable full debug

Enable full debug as follows:

$ sudo mkdir -p /etc/kata-containers/
$ sudo install -o root -g root -m 0640 /usr/share/defaults/kata-containers/configuration.toml /etc/kata-containers
$ sudo sed -i -e 's/^# *\(enable_debug\).*=.*$/\1 = true/g' /etc/kata-containers/configuration.toml
$ sudo sed -i -e 's/^kernel_params = "\(.*\)"/kernel_params = "\1 agent.log=debug initcall_debug"/g' /etc/kata-containers/configuration.toml

journald rate limiting

Enabling full debug results in the Kata components generating large amounts of logging, which by default is stored in the system log. Depending on your system configuration, it is possible that some events might be discarded by the system logging daemon. The following shows how to determine this for systemd-journald, and offers possible workarounds and fixes.

Note The method of implementation can vary between Operating System installations. Amend these instructions as necessary to your system implementation, and consult with your system administrator for the appropriate configuration.

systemd-journald suppressing messages

systemd-journald can be configured to rate limit the number of journal entries it stores. When messages are suppressed, it is noted in the logs. This can be checked for by looking for those notifications, such as:

$ sudo journalctl --since today | fgrep Suppressed
Jun 29 14:51:17 mymachine systemd-journald[346]: Suppressed 4150 messages from /system.slice/docker.service

This message indicates that a number of log messages from the docker.service slice were suppressed. In such a case, you can expect to have incomplete logging information stored from the Kata Containers components.

Disabling systemd-journald rate limiting

In order to capture complete logs from the Kata Containers components, you need to reduce or disable the systemd-journald rate limit. Configure this at the global systemd-journald level, and it will apply to all system slices.

To disable systemd-journald rate limiting at the global level, edit the file /etc/systemd/journald.conf, and add/uncomment the following lines:

RateLimitInterval=0s
RateLimitBurst=0

Restart systemd-journald for the changes to take effect:

$ sudo systemctl restart systemd-journald

Build and install Kata proxy

$ go get -d -u github.com/kata-containers/proxy
$ cd $GOPATH/src/github.com/kata-containers/proxy && make && sudo make install

Build and install Kata shim

$ go get -d -u github.com/kata-containers/shim
$ cd $GOPATH/src/github.com/kata-containers/shim && make && sudo make install

Create and install rootfs and initrd image

Build a custom Kata agent - OPTIONAL

Note:

  • You should only do this step if you are testing with the latest version of the agent.
$ go get -d -u github.com/kata-containers/agent
$ cd $GOPATH/src/github.com/kata-containers/agent && make

Get the osbuilder

$ go get -d -u github.com/kata-containers/osbuilder

Create a rootfs image

Create a local rootfs

As a prerequisite, you need to install Docker. Otherwise, you will not be able to run the rootfs.sh script with USE_DOCKER=true as expected in the following example.

$ export ROOTFS_DIR=${GOPATH}/src/github.com/kata-containers/osbuilder/rootfs-builder/rootfs
$ sudo rm -rf ${ROOTFS_DIR}
$ cd $GOPATH/src/github.com/kata-containers/osbuilder/rootfs-builder
$ script -fec 'sudo -E GOPATH=$GOPATH USE_DOCKER=true SECCOMP=no ./rootfs.sh ${distro}'

You MUST choose one of alpine, centos, clearlinux, euleros, and fedora for ${distro}. By default seccomp packages are not included in the rootfs image. Set SECCOMP to yes to include them.

Note:

  • Check the compatibility matrix before creating rootfs.
  • You must ensure that the default Docker runtime is runc to make use of the USE_DOCKER variable. If that is not the case, remove the variable from the previous command. See Checking Docker default runtime.

Add a custom agent to the image - OPTIONAL

Note:

  • You should only do this step if you are testing with the latest version of the agent.
$ sudo install -o root -g root -m 0550 -t ${ROOTFS_DIR}/bin ../../agent/kata-agent
$ sudo install -o root -g root -m 0440 ../../agent/kata-agent.service ${ROOTFS_DIR}/usr/lib/systemd/system/
$ sudo install -o root -g root -m 0440 ../../agent/kata-containers.target ${ROOTFS_DIR}/usr/lib/systemd/system/

Build a rootfs image

$ cd $GOPATH/src/github.com/kata-containers/osbuilder/image-builder
$ script -fec 'sudo -E USE_DOCKER=true ./image_builder.sh ${ROOTFS_DIR}'

Notes:

  • You must ensure that the default Docker runtime is runc to make use of the USE_DOCKER variable. If that is not the case, remove the variable from the previous command. See Checking Docker default runtime.
  • If you do not wish to build under Docker, remove the USE_DOCKER variable in the previous command and ensure the qemu-img command is available on your system.

Install the rootfs image

$ commit=$(git log --format=%h -1 HEAD)
$ date=$(date +%Y-%m-%d-%T.%N%z)
$ image="kata-containers-${date}-${commit}"
$ sudo install -o root -g root -m 0640 -D kata-containers.img "/usr/share/kata-containers/${image}"
$ (cd /usr/share/kata-containers && sudo ln -sf "$image" kata-containers.img)

Create an initrd image - OPTIONAL

Create a local rootfs for initrd image

$ export ROOTFS_DIR="${GOPATH}/src/github.com/kata-containers/osbuilder/rootfs-builder/rootfs"
$ sudo rm -rf ${ROOTFS_DIR}
$ cd $GOPATH/src/github.com/kata-containers/osbuilder/rootfs-builder
$ script -fec 'sudo -E GOPATH=$GOPATH AGENT_INIT=yes USE_DOCKER=true SECCOMP=no ./rootfs.sh ${distro}'

AGENT_INIT controls if the guest image uses the Kata agent as the guest init process. When you create an initrd image, always set AGENT_INIT to yes. By default seccomp packages are not included in the initrd image. Set SECCOMP to yes to include them.

You MUST choose one of alpine, centos, clearlinux, euleros, and fedora for ${distro}.

Note:

Optionally, add your custom agent binary to the rootfs with the following:

$ sudo install -o root -g root -m 0550 -T ../../agent/kata-agent ${ROOTFS_DIR}/sbin/init

Build an initrd image

$ cd $GOPATH/src/github.com/kata-containers/osbuilder/initrd-builder
$ script -fec 'sudo -E AGENT_INIT=yes USE_DOCKER=true ./initrd_builder.sh ${ROOTFS_DIR}'

Install the initrd image

$ commit=$(git log --format=%h -1 HEAD)
$ date=$(date +%Y-%m-%d-%T.%N%z)
$ image="kata-containers-initrd-${date}-${commit}"
$ sudo install -o root -g root -m 0640 -D kata-containers-initrd.img "/usr/share/kata-containers/${image}"
$ (cd /usr/share/kata-containers && sudo ln -sf "$image" kata-containers-initrd.img)

Install guest kernel images

You can build and install the guest kernel image as shown here.

Install a hypervisor

When setting up Kata using a packaged installation method, the qemu-lite hypervisor is installed automatically. For other installation methods, you will need to manually install a suitable hypervisor.

Build a custom QEMU

Your QEMU directory need to be prepared with source code. Alternatively, you can use the Kata containers QEMU and checkout the recommended branch:

$ go get -d github.com/kata-containers/qemu
$ qemu_branch=$(grep qemu-lite- ${GOPATH}/src/github.com/kata-containers/runtime/versions.yaml | cut -d '"' -f2)
$ cd ${GOPATH}/src/github.com/kata-containers/qemu
$ git checkout -b $qemu_branch remotes/origin/$qemu_branch
$ your_qemu_directory=${GOPATH}/src/github.com/kata-containers/qemu

To build a version of QEMU using the same options as the default qemu-lite version , you could use the configure-hypervisor.sh script:

$ go get -d github.com/kata-containers/packaging
$ cd $your_qemu_directory
$ ${GOPATH}/src/github.com/kata-containers/packaging/scripts/configure-hypervisor.sh qemu > kata.cfg
$ eval ./configure "$(cat kata.cfg)"
$ make -j $(nproc)
$ sudo -E make install

Build a custom QEMU for aarch64/arm64 - REQUIRED

Note:

You could build the custom qemu-system-aarch64 as required with the following command:

$ go get -d github.com/kata-containers/tests
$ script -fec 'sudo -E ${GOPATH}/src/github.com/kata-containers/tests/.ci/install_qemu.sh'

Run Kata Containers with Docker

Update the Docker systemd unit file

$ dockerUnit=$(systemctl show -p FragmentPath docker.service | cut -d "=" -f 2)
$ unitFile=${dockerUnit:-/etc/systemd/system/docker.service.d/kata-containers.conf}
$ test -e "$unitFile" || { sudo mkdir -p "$(dirname $unitFile)"; echo -e "[Service]\nType=simple\nExecStart=\nExecStart=/usr/bin/dockerd -D --default-runtime runc" | sudo tee "$unitFile"; }
$ grep -q "kata-runtime=" $unitFile || sudo sed -i 's!^\(ExecStart=[^$].*$\)!\1 --add-runtime kata-runtime=/usr/local/bin/kata-runtime!g' "$unitFile"
$ sudo systemctl daemon-reload
$ sudo systemctl restart docker

Create a container using Kata

$ sudo docker run -ti --runtime kata-runtime busybox sh

Run Kata Containers with Kubernetes

Now that Kata Containers is installed on your system, you need some extra components to make this work with Kubernetes.

Install a CRI implementation

Kata Containers runtime is an OCI compatible runtime and cannot directly interact with the CRI API level. For this reason we rely on a CRI implementation to translate CRI into OCI. There are two supported ways called CRI-O and CRI-containerd. It is up to you to choose the one that you want, but you have to pick one. After choosing either CRI-O or CRI-containerd, you must make the appropriate changes to ensure it relies on the Kata Containers runtime.

As of Kata Containers 1.5, using shimv2 with containerd 1.2.0 or above is the preferred way to run Kata Containers with Kubernetes (see the howto). The CRI-O will catch up soon.

CRI-O

If you select CRI-O, follow the "CRI-O Tutorial" instructions here to properly install it.

Once you have installed CRI-O, you need to modify the CRI-O configuration with information about different container runtimes. By default, we choose runc, but in this case we also specify Kata Containers runtime to run untrusted workloads. In other words, this defines an alternative runtime to be used when the workload cannot be trusted and a higher level of security is required. An additional flag can be used to let CRI-O know if a workload should be considered trusted or untrusted by default. For further details, see the documentation here.

Additionally, we need CRI-O to perform the network namespace management. Otherwise, when the VM starts the network will not be available.

The following is an example of how to modify the /etc/crio/crio.conf file in order to apply the previous explanations, and therefore get Kata Containers runtime to invoke by CRI-O.

# The "crio.runtime" table contains settings pertaining to the OCI
# runtime used and options for how to set up and manage the OCI runtime.
[crio.runtime]
manage_network_ns_lifecycle = true

# runtime is the OCI compatible runtime used for trusted container workloads.
# This is a mandatory setting as this runtime will be the default one
# and will also be used for untrusted container workloads if
# runtime_untrusted_workload is not set.
runtime = "/usr/bin/runc"

# runtime_untrusted_workload is the OCI compatible runtime used for untrusted
# container workloads. This is an optional setting, except if
# default_container_trust is set to "untrusted".
runtime_untrusted_workload = "/usr/bin/kata-runtime"

# default_workload_trust is the default level of trust crio puts in container
# workloads. It can either be "trusted" or "untrusted", and the default
# is "trusted".
# Containers can be run through different container runtimes, depending on
# the trust hints we receive from kubelet:
# - If kubelet tags a container workload as untrusted, crio will try first to
# run it through the untrusted container workload runtime. If it is not set,
# crio will use the trusted runtime.
# - If kubelet does not provide any information about the container workload trust
# level, the selected runtime will depend on the default_container_trust setting.
# If it is set to "untrusted", then all containers except for the host privileged
# ones, will be run by the runtime_untrusted_workload runtime. Host privileged
# containers are by definition trusted and will always use the trusted container
# runtime. If default_container_trust is set to "trusted", crio will use the trusted
# container runtime for all containers.
default_workload_trust = "untrusted"

Restart CRI-O to take changes into account

$ sudo systemctl restart crio

containerd with CRI plugin

If you select containerd with cri plugin, follow the "Getting Started for Developers" instructions here to properly install it.

To customize containerd to select Kata Containers runtime, follow our "Configure containerd to use Kata Containers" internal documentation here.

Install Kubernetes

Depending on what your needs are and what you expect to do with Kubernetes, please refer to the following documentation to install it correctly.

Kubernetes talks with CRI implementations through a container-runtime-endpoint, also called CRI socket. This socket path is different depending on which CRI implementation you chose, and the Kubelet service has to be updated accordingly.

Configure for CRI-O

/etc/systemd/system/kubelet.service.d/0-crio.conf

[Service]
Environment="KUBELET_EXTRA_ARGS=--container-runtime=remote --runtime-request-timeout=15m --container-runtime-endpoint=unix:///var/run/crio/crio.sock"

Configure for containerd

/etc/systemd/system/kubelet.service.d/0-cri-containerd.conf

[Service]
Environment="KUBELET_EXTRA_ARGS=--container-runtime=remote --runtime-request-timeout=15m --container-runtime-endpoint=unix:///run/containerd/containerd.sock"

For more information about containerd see the "Configure Kubelet to use containerd" documentation here.

Run a Kubernetes pod with Kata Containers

After you update your Kubelet service based on the CRI implementation you are using, reload and restart Kubelet. Then, start your cluster:

$ sudo systemctl daemon-reload
$ sudo systemctl restart kubelet

# If using CRI-O
$ sudo kubeadm init --skip-preflight-checks --cri-socket /var/run/crio/crio.sock --pod-network-cidr=10.244.0.0/16

# If using CRI-containerd
$ sudo kubeadm init --skip-preflight-checks --cri-socket /run/containerd/containerd.sock --pod-network-cidr=10.244.0.0/16

$ export KUBECONFIG=/etc/kubernetes/admin.conf

You can force Kubelet to use Kata Containers by adding some untrusted annotation to your pod configuration. In our case, this ensures Kata Containers is the selected runtime to run the described workload.

nginx-untrusted.yaml

apiVersion: v1
kind: Pod
metadata:
  name: nginx-untrusted
  annotations:
    io.kubernetes.cri.untrusted-workload: "true"
spec:
  containers:
    - name: nginx
      image: nginx

Next, you run your pod:

$ sudo -E kubectl apply -f nginx-untrusted.yaml

Troubleshoot Kata Containers

If you are unable to create a Kata Container first ensure you have enabled full debug before attempting to create a container. Then run the kata-collect-data.sh script and paste its output directly into a GitHub issue.

Note:

The kata-collect-data.sh script is built from the runtime repository.

To perform analysis on Kata logs, use the kata-log-parser tool, which can convert the logs into formats (e.g. JSON, TOML, XML, and YAML).

To obtain a full backtrace for the agent, proxy, runtime, or shim send the SIGUSR1 signal to the process ID of the component. The component will send a backtrace to the system log on the host system and continue to run without interruption.

For example, to obtain a backtrace for kata-proxy:

$ sudo kill -USR1 $kata_proxy_pid
$ sudo journalctl -t kata-proxy

See Set up a debug console.

Appendices

Checking Docker default runtime

$ sudo docker info 2>/dev/null | grep -i "default runtime" | cut -d: -f2- | grep -q runc  && echo "SUCCESS" || echo "ERROR: Incorrect default Docker runtime"

Set up a debug console

By default you cannot login to a virtual machine, since this can be sensitive from a security perspective. Also, allowing logins would require additional packages in the rootfs, which would increase the size of the image used to boot the virtual machine.

If you want to login to a virtual machine that hosts your containers, complete the following steps, which assume the use of a rootfs image.

Note: The following debug console instructions assume a systemd-based guest O/S image. This means you must create a rootfs for a distro that supports systemd. Currently, all distros supported by osbuilder support systemd except for Alpine Linux.

Look for INIT_PROCESS=systemd in the config.sh osbuilder rootfs config file to verify an osbuilder distro supports systemd for the distro you want to build rootfs for. For an example, see the Clear Linux config.sh file.

For a non-systemd-based distro, create an equivalent system service using that distro’s init system syntax. Alternatively, you can build a distro that contains a shell (e.g. bash(1)). In this circumstance it is likely you need to install additional packages in the rootfs and add “agent.debug_console” to kernel parameters in the runtime config file. This tells the Kata agent to launch the console directly.

Once these steps are taken you can connect to the virtual machine using the debug console.

Create a custom image containing a shell

To login to a virtual machine, you must create a custom rootfs containing a shell such as bash(1). For Clear Linux, you will need an additional coreutils package.

For example using CentOS:

$ cd $GOPATH/src/github.com/kata-containers/osbuilder/rootfs-builder
$ export ROOTFS_DIR=${GOPATH}/src/github.com/kata-containers/osbuilder/rootfs-builder/rootfs
$ script -fec 'sudo -E GOPATH=$GOPATH USE_DOCKER=true EXTRA_PKGS="bash coreutils" ./rootfs.sh centos'

Create a debug systemd service

Create the service file that starts the shell in the rootfs directory:

$ cat <<EOT | sudo tee ${ROOTFS_DIR}/lib/systemd/system/kata-debug.service
[Unit]
Description=Kata Containers debug console

[Service]
Environment=PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
StandardInput=tty
StandardOutput=tty
# Must be disabled to allow the job to access the real console
PrivateDevices=no
Type=simple
ExecStart=/bin/bash
Restart=always
EOT

Note: You might need to adjust the ExecStart= path.

Add a dependency to start the debug console:

$ sudo sed -i '$a Requires=kata-debug.service' ${ROOTFS_DIR}/lib/systemd/system/kata-containers.target

Build the debug image

Follow the instructions in the Build a rootfs image section.

Configure runtime for custom debug image

Install the image:

$ name="kata-containers-centos-with-debug-console.img"
$ sudo install -o root -g root -m 0640 kata-containers.img "/usr/share/kata-containers/${name}"

Next, modify the image= values in the [hypervisor.qemu] section of the configuration file to specify the full path to the image name specified in the previous code section. Alternatively, recreate the symbolic link so it points to the new debug image:

$ (cd /usr/share/kata-containers && sudo ln -sf "$name" kata-containers.img)

Note: You should take care to undo this change after you finish debugging to avoid all subsequently created containers from using the debug image.

Ensure debug options are valid

For the debug console to work, you must ensure that proxy debug is disabled in the configuration file. If proxy debug is enabled, you will not see any output when you connect to the virtual machine:

$ sudo mkdir -p /etc/kata-containers/
$ sudo install -o root -g root -m 0640 /usr/share/defaults/kata-containers/configuration.toml /etc/kata-containers
$ sudo awk '{if (/^\[proxy\.kata\]/) {got=1}; if (got == 1 && /^.*enable_debug/) {print "#enable_debug = true"; got=0; next; } else {print}}' /etc/kata-containers/configuration.toml > /tmp/configuration.toml
$ sudo install -o root -g root -m 0640 /tmp/configuration.toml /etc/kata-containers/

Create a container

Create a container as normal. For example using Docker:

$ sudo docker run -ti busybox sh

Connect to the virtual machine using the debug console

$ id=$(sudo docker ps -q --no-trunc)
$ console="/var/run/vc/vm/${id}/console.sock"
$ sudo socat "stdin,raw,echo=0,escape=0x11" "unix-connect:${console}"

Note: You need to press the RETURN key to see the shell prompt.

To disconnect from the virtual machine, type CONTROL+q (hold down the CONTROL key and press q).

Obtain details of the image

If the image is created using osbuilder, the following YAML file exists and contains details of the image and how it was created:

$ cat /var/lib/osbuilder/osbuilder.yaml

Running standalone

It is possible to start the runtime without a container manager. This is mostly useful for testing and debugging purposes.

Create an OCI bundle

To build an OCI bundle, required by the runtime:

$ bundle="/tmp/bundle"
$ rootfs="$bundle/rootfs"
$ mkdir -p "$rootfs" && (cd "$bundle" && kata-runtime spec)
$ sudo docker export $(sudo docker create busybox) | tar -C "$rootfs" -xvf -

Launch the runtime to create a container

Run the runtime standalone by providing it with the path to the previously-created OCI bundle:

$ sudo kata-runtime --log=/dev/stdout run --bundle "$bundle" foo