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CH Show HN: Kdo – Deployless Development on Kubernetes

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Kdo is a command line tool that enables developers to run, develop and test code changes in a realistic deployed setting without having to deal with the complexity of Kubernetes deployment and configuration.

With Kdo, you can:

  • run a command in a Kubernetes cluster without any deployment;
  • build and use a custom image to run a command without any registry;
  • inherit pod configuration from an existing workload instead of deploying;
  • replace existing pods while running a command to evaluate end-to-end behavior.

Kdo can also be used for longer-running connected development sessions where local file updates are pushed into the running container, enabling rapid iteration on code while continuing to run as a properly configured container in the Kubernetes cluster.

Prerequisites and Installation

Kdo requires the kubectl CLI to communicate with a Kubernetes cluster and the docker CLI to perform dynamic image builds, so first make sure you have these installed and available in your PATH. Then, download the latest release for your platform and add the kdo binary to your PATH.

By default kdo utilizes the current kubectl context, so point it at the Kubernetes cluster of your choice and you’re good to go!

Quickstart

Take a look at the TODO application sample.

Examples

Run a command shell in an alpine container:

kdo -it alpine

Run a DNS lookup in an alpine container:

kdo -it alpine nslookup kubernetes.default.svc.cluster.local

Run a Node.js app in a container built from the current directory:

kdo . npm start

Run the default command in a container built from the current directory that inherits configuration from the first container defined by the pod template in the todo-app deployment spec:

kdo -c deployment/todo-app .

Run a command shell in a container built from the current directory that inherits existing configuration from the first container defined by the first pod selected by the todo-app service, and also push any changes in the current directory to the container’s /app directory:

kdo -c service/todo-app -s .:/app -it . sh

Debug a Node.js app in a container built from the current directory that inherits existing configuration from the first container defined by the todo-app-56db-xdhfx pod, and forward TCP connections made to local ports 8080 and 9229 to container ports 80 and 9229 respectively:

kdo -c todo-app-56db-xdhfx -p 8080:80 -p 9229:9229 . node --inspect-brk=0.0.0.0:9229 server.js

Run the default command in a kdo-samples/todo-app container that inherits its configuration from the web container defined by the pod template in the todo-app deployment spec, and also overlay any existing pods produced by that same deployment:

kdo -c deployment/todo-app:web -R kdo-samples/todo-app

Usage

Kdo is a single command CLI that can be called in a small number of unique ways:

kdo [flags] image [command] [args...]
kdo [flags] build-dir [command] [args...]
kdo --[un]install [-q, --quiet] [-v, --verbose] [--debug]
kdo --version | --help

When called with an image parameter, this represents an existing image to be run in the Kubernetes cluster. This is distinguished from the build-dir parameter, which always starts with . and identifies a local build context for a custom image to run in the Kubernetes cluster.

When the command parameter is set, this configures the command property in the container and removes the args property.

When called with the --install or --uninstall flag, all other flags with the exception of those listed above are ignored and no positional parameters are allowed.

Flags

Kdo can be customized in a variety of ways through a set of command line flags.

Kubernetes flags

These flags customize how the kubectl CLI is used.

Flag Default Description
--kubectl kubectl path to the kubectl CLI
--kubeconfig path to the kubeconfig file to use
--context the kubeconfig context to use
-n, --namespace the kubernetes namespace to use
--kubectl-v 0 the kubectl log level verbosity

Installation flags

These flags are used to manage the kdo server components. These components are installed into the kube-system namespace as a daemon set, so using these flags requires administrative access to the Kubernetes cluster.

Flag Description
--install install server components and exit
--uninstall uninstall server components and exit

Normally the server components are installed automatically as needed, but this is not possible if the user does not have permission to install into the kube-system namespace. In that case, an alternative administrative user can use the --install flag to manually configure the cluster for other users.

The --uninstall flag can be used to explicitly remove any leftover kdo pods across all namespaces in addition to the server components from a cluster.

Scope flag

The scope flag (--scope) can be used to change how Kubernetes cluster resources are uniquely named. By default, the local machine’s hostname is used.

Build flags

These flags customize how the docker CLI is used when building images.

Flag Default Description
--docker docker path to the docker CLI
--docker-config path to the docker CLI config files
--docker-log-level the docker CLI logging level
-f, --build-file /Dockerfile dockerfile to build
--build-arg [] build-time variables in the form name=value
--build-target dockerfile target to build

When the docker CLI is invoked, it does not use the default configured Docker daemon. Instead, it uses the kdo server components to directly access the Docker daemon running on a node in the Kubernetes cluster. Therefore, it is theoretically not a requirement that the local machine is actually running Docker, although in most cases (e.g. Docker Desktop) this will be the case. It is, however, a requirement that the node on which the kdo pod is scheduled is using Docker for its container runtime and the Docker daemon socket at /var/run/docker.sock on the host can be volume mounted into the pod.

Configuration flags

These flags customize the pod and container that runs the command.

Flag Default Description
-c, --inherit inherit an existing configuration
-L, --inherit-labels false inherit pod labels
-A, --inherit-annotations false inherit pod annotations
--label [] inherit, set or remove pod labels in the form name[=[value]]
--annotate [] inherit, set or remove pod annotations in the form name[=[value]]
-e, --env [] set container environment variables in the form name=value
--no-lifecycle false do not inherit container lifecycle
--no-probes false do not inherit container probes

The -c, --inherit flag inherits an existing configuration and selects a container in the form [kind/]name[:container], where kind is a Kubernetes workload kind (cronjob, daemonset, deployment, job, pod, replicaset, replicationcontroller or statefulset) or service (default is pod). If the kind is not pod, the pod spec is based on the template in the outer workload spec, except in the case of service, when it is based on the workload that originally generated the first pod selected by the service. If container is not specified, the first container in the pod spec is selected. Init containers are not supported.

By default, when inheriting an existing configuration, pod labels and annotations are not inherited to prevent the Kubernetes cluster from misunderstanding the role of the pod (for instance, automatically being added as an instance behind a service). The --inherit-labels and/or --inherit-annotations flags can be used to override this behavior.

Whether or not labels or annotations are inherited, the final set of label or annotation entries can be customized using the --label and --annotate flags. If a value is simply in the form name, then its entry is inherited. If a value is in the form name=value, it adds or overrides any existing entry. Lastly, if a value is in the form name=, it removes an entry that may otherwise be inherited.

The -e, --env flags set container environment variables, and in the case of an inherited configuration, override any inherited environment variables.

When inheriting an existing configuration, there are cases when the existing container lifecycle and probe configuration are not implemented, would cause problems, or are entirely irrelevant for the scenario. The --no-lifecyle and --no-probes flags can be used to ensure these properties are not inherited.

Replace flag

The -R, --replace flag overlays an inherited configuration’s workload. This flag only applies when the inherited configuration is from the deployment, replicaset, replicationcontroller and statefulset workload kinds, or from the service kind. For workloads, this flag scales the workload instance to zero for the duration of the command. For services, this flag changes the pod selector to select the kdo pod for the duration of the command.

Session flags

These flags customize behavior that applies for the duration of the kdo process.

Flag Default Description
-s, --sync [] push local file changes to the container in the form [localdir:]remotedir
-p, --forward [] forward local ports to container ports in the form [local:]remote
-l, --listen [] forward container ports to local ports in the form remote[:local]

The -s, --sync flag is only valid when using the build-dir parameter. It enables synchronization of changes in directories under the local build context into an appropriate directory in the container. For example, --sync /app synchronizes the entire build context to the /app directory in the container, while --sync src:/app/src synchronizes only the src directory to the /app/src directory in the container. The local directory must be relative to the build context and defaults to ., while the remote directory must be an absolute path to a directory in the container.

The -p, --forward flag enables the local machine to access specific container ports, for example, --forward 8080:80 will forward local port 8080 to container port 80.

The -l, --listen flag enables code running in the container to access specific localhost ports that are forwarded back to the local machine. This can be used to replace external dependencies, such as data stores, used by the code running in the container, with an alternate endpoint on the local machine. For instance:

# Start a local Mongo database that can be accessed at localhost:27017
docker run -p 27017:27017 -d mongo:4

# Build and run a web server image in Kubernetes, forwarding local port
# 8080 to container port 80, and when the web server code connects to a
# Mongo database using the MONGO_CONNECTION_STRING environment variable,
# proxy the connection back to local port 27017.
kdo -p 8080:80 -e MONGO_CONNECTION_STRING=localhost:27017 -l 27017:27017 .

The -s, --sync, -p, --forward and -l, --listen flags cannot be combined with the -d, --detach flag.

Command flags

These flags customize how the command is run.

Flag Default Description
-x, --exec false execute command in an existing pod
-k, --prekill [] kill existing processes prior to an exec
-i, --stdin false connect standard input to the container
-t, --tty false allocate a pseudo-TTY in the container

When using the -x, --exec flag, build, configuration and session flags are ignored with the exception of the -c, --inherit flag which is used to help identify the target container, and the -p, --forward flag. Additionally, this flag cannot be combined with the -d, --detach or --delete flags.

The -k, --prekill flag can be used with the -x, --exec flag to pre-kill existing processes by name that may be running in the container. This requires the pkill command in the container, and it sends a SIGKILL to all processes matching the specified flag values.

Detach flags

These flags relate to running a pod in the background.

Flag Default Description
-d, --detach false run pod in the background
--delete false delete a previously detached pod
--delete-all false delete all previously detached pods

These flags cannot be combined.

Output flags

These flags customize how kdo outputs information.

Flag Default Description
-q, --quiet false output no information
-v, --verbose false output more information
--debug false output debug information

If multiple of these flags are specified, the -q, --quiet takes highest precedence, followed by the --debug and -v, --verbose flags in that order.

Other flags

Flag Default Description
--version false show version information
--help false show help information

License

Kdo is licensed under the MIT license.

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