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diff --git a/docs/tutorials/README.md b/docs/tutorials/README.md index 191d7a4b5..4beb069ac 100644 --- a/docs/tutorials/README.md +++ b/docs/tutorials/README.md @@ -27,3 +27,7 @@ How the libpod API can be used within your own project. **[Image Signing](image_signing.md)** Learn how to setup and use image signing with Podman. + +**[Go Bindings](podman-go-bindings.md)** + +A brief how-to on using Podman's Go bindings in external applications. diff --git a/docs/tutorials/podman-go-bindings.md b/docs/tutorials/podman-go-bindings.md new file mode 100644 index 000000000..ddebf7e99 --- /dev/null +++ b/docs/tutorials/podman-go-bindings.md @@ -0,0 +1,546 @@ + + +# Podman Go bindings + +## Introduction + +In the release of Podman 2.0, we removed the experimental tag +from its recently introduced RESTful service. While it might +be interesting to interact with a RESTFul server using curl, +using a set of Go based bindings is probably a more direct +route to a production ready application. Let’s take a look +at how easily that can be accomplished. + +If you haven't yet, [install Go](https://golang.org/doc/install). + +Be careful to double-check that the version of golang is new +enough (i.e. `go version`), version 1.13.x or higher is +supported. If needed, Go sources and binaries can be fetched +from the [official Go website](https://golang.org/dl/). + +The Podman Go bindings are a set of functions to allow +developers to execute Podman operations from within their Go +based application. The Go bindings connect to a Podman service +which can run locally or on a remote machine. You can perform +many operations including pulling and listing images, starting, +stopping or inspecting containers. Currently, the Podman +repository has bindings available for operations on images, +containers, pods, networks and manifests among others. The +bindings are available on the [v2.0 branch in the +upstream Podman repository](https://github.com/containers/podman/tree/v2.0). +You can fetch the bindings for your application using Go modules: + +```bash +$ cd $HOME +$ mkdir example && cd example +$ go mod init example.com +go: creating new go.mod: module example.com +$ go get github.com/containers/podman/v2@v2.0.4 +go: downloading github.com/containers/podman/v2 v2.0.4 +go get: github.com/containers/podman/v2@v2.0.4: parsing go.mod: + module declares its path as: github.com/containers/libpod/v2 + but was required as: github.com/containers/podman/v2 +``` + +This creates a new `go.mod` file in the current directory that looks as follows: + +```bash +module example.com + +go 1.14 + +require github.com/containers/libpod/v2 v2.0.4 // indirect +``` + +You can also try a demo application with the Go modules created already: + +```bash +$ git clone https://github.com/containers/Demos +$ cd Demos/podman_go_bindings +$ ls +README.md go.mod go.sum main.go +``` + + +## How do I use them + +In this tutorial, you will learn through basic examples how to: + +0. [Start the Podman system service](#start-service) +1. [Connect to the Podman system service](#connect-service) +2. [Pull images](#pull-images) +3. [List images](#list-images) +4. [Create and start a container from an image](#create-start-container) +5. [List containers](#list-containers) +6. [Inspect the container](#inspect-container) +7. [Stop the container](#stop-container) +8. [Debugging tips](#debugging-tips) + + +### Start the Podman system service <a name="start-service"></a> +The recommended way to start Podman system service in production mode +is via systemd socket-activation: + +```bash +$ systemctl --user start podman.socket +``` + +There’s no timeout specified when starting the system service via socket-activation. + +For purposes of this demo, we will start the service using the Podman +command itself. If you prefer the system service to timeout after, say, +5000 seconds, you can run it like so: + +```bash +$ podman system service -t 5000 +``` + +Note that the 5000 seconds uptime is refreshed after every command is received. +If you want the service to stay up until the machine is shutdown or the process +is terminated, use `0` (zero) instead of 5000. For this demo, we will use no timeout: + +```bash +$ podman system service -t 0 +``` + + +Open another terminal window and check if the Podman socket exists: + +```bash +$ ls /run/user/${UID}/podman +podman.sock +``` + +If you’re running the system service as root, podman.sock will be found in /run/podman: +```bash +# ls /run/podman +podman.sock +``` + + +### Connect to the Podman system service <a name="connect-service"></a> +First, you need to create a connection that connects to the system service. +The critical piece of information for setting up a new connection is the endpoint. +The endpoint comes in the form of an URI (method:/path/to/socket). For example, +to connect to the local rootful socket the URI would be `unix:/run/podman/podman.sock` +and for a rootless user it would be `unix:$(XDG_RUNTIME_DIR)/podman/podman.sock`, +typically: `unix:/run/user/${UID}/podman/podman.sock`. + + +The following Go example snippet shows how to set up a connection for a rootless user. +```Go +package main + +import ( + "context" + "fmt" + "os" + + "github.com/containers/libpod/v2/libpod/define" + "github.com/containers/libpod/v2/pkg/bindings" + "github.com/containers/libpod/v2/pkg/bindings/containers" + "github.com/containers/libpod/v2/pkg/bindings/images" + "github.com/containers/libpod/v2/pkg/domain/entities" + "github.com/containers/libpod/v2/pkg/specgen" +) + +func main() { + fmt.Println("Welcome to the Podman Go bindings tutorial") + + // Get Podman socket location + sock_dir := os.Getenv("XDG_RUNTIME_DIR") + socket := "unix:" + sock_dir + "/podman/podman.sock" + + // Connect to Podman socket + connText, err := bindings.NewConnection(context.Background(), socket) + if err != nil { + fmt.Println(err) + os.Exit(1) + } +} +``` + +The `connText` variable received from the NewConnection function is of type +context.Context(). In subsequent uses of the bindings, you will use this context +to direct the bindings to your connection. This can be seen in the examples below. + +### Pull an image <a name="pull-images"></a> + +Next, we will pull a couple of images using the images.Pull() binding. +This binding takes three arguments: + - The context variable created by the bindings.NewConnection() call in the first example + - The image name + - Options for image pull + +**Append the following lines to your function:** + +```Go + // Pull Busybox image (Sample 1) + fmt.Println("Pulling Busybox image...") + _, err = images.Pull(connText, "docker.io/busybox", entities.ImagePullOptions{}) + if err != nil { + fmt.Println(err) + os.Exit(1) + } + + // Pull Fedora image (Sample 2) + rawImage := "registry.fedoraproject.org/fedora:latest" + fmt.Println("Pulling Fedora image...") + _, err = images.Pull(connText, rawImage, entities.ImagePullOptions{}) + if err != nil { + fmt.Println(err) + os.Exit(1) + } +``` + +**Run it:** + +```bash +$ go run main.go +Welcome to the Podman Go bindings tutorial +Pulling Busybox image... +Pulling Fedora image... +$ +``` + +The system service side should echo messages like so: + +```bash +Trying to pull docker.io/busybox... +Getting image source signatures +Copying blob 61c5ed1cbdf8 [--------------------------------------] 0.0b / 0.0b +Copying config 018c9d7b79 done +Writing manifest to image destination +Storing signatures +Trying to pull registry.fedoraproject.org/fedora:latest... +Getting image source signatures +Copying blob dd9f43919ba0 [--------------------------------------] 0.0b / 0.0b +Copying config 00ff39a8bf done +Writing manifest to image destination +Storing signatures +``` + + +### List images <a name="list-images"></a> +Next, we will pull an image using the images.List() binding. +This binding takes three arguments: + - The context variable created earlier + - An optional bool 'all' + - An optional map of filters + +**Append the following lines to your function:** + +```Go + // List images + imageSummary, err := images.List(connText, nil, nil) + if err != nil { + fmt.Println(err) + os.Exit(1) + } + var names []string + for _, i := range imageSummary { + names = append(names, i.RepoTags...) + } + fmt.Println("Listing images...") + fmt.Println(names) +``` + +**Run it:** + +```bash +$ go run main.go +Welcome to the Podman Go bindings tutorial +Pulling Busybox image... +Pulling Fedora image... +Listing images... +[docker.io/library/busybox:latest registry.fedoraproject.org/fedora:latest] +$ +``` + + +### Create and Start a Container from an Image <a name="create-start-container"></a> + +To create the container spec, we use specgen.NewSpecGenerator() followed by +calling containers.CreateWithSpec() to actually create a new container. +specgen.NewSpecGenerator() takes 2 arguments: + - name of the image + - whether it's a rootfs + +containers.CreateWithSpec() takes 2 arguments: + - the context created earlier + - the spec created by NewSpecGenerator + +Next, the container is actually started using the containers.Start() binding. +containers.Start() takes three arguments: + - the context + - the name or ID of the container created + - an optional parameter for detach keys + +After the container is started, it's a good idea to ensure the container is +in a running state before you proceed with further operations. +The containers.Wait() takes care of that. +containers.Wait() takes three arguments: + - the context + - the name or ID of the container created + - container state (running/paused/stopped) + +**Append the following lines to your function:** + +```Go + // Container create + s := specgen.NewSpecGenerator(rawImage, false) + s.Terminal = true + r, err := containers.CreateWithSpec(connText, s) + if err != nil { + fmt.Println(err) + os.Exit(1) + } + + // Container start + fmt.Println("Starting Fedora container...") + err = containers.Start(connText, r.ID, nil) + if err != nil { + fmt.Println(err) + os.Exit(1) + } + + running := define.ContainerStateRunning + _, err = containers.Wait(connText, r.ID, &running) + if err != nil { + fmt.Println(err) + os.Exit(1) + } +``` + +**Run it:** + +```bash +$ go run main.go +Welcome to the Podman Go bindings tutorial +Pulling image... +Starting Fedora container... +$ +``` + +Check if the container is running: + +```bash +$ podman ps +CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES +665831d31e90 registry.fedoraproject.org/fedora:latest /bin/bash Less than a second ago Up Less than a second ago dazzling_mclean +$ +``` + + +### List Containers <a name="list-containers"></a> + +Containers can be listed using the containers.List() binding. +containers.List() takes seven arguments: + - the context + - output filters + - boolean to show all containers, by default only running containers are listed + - number of latest created containers, all states (running/paused/stopped) + - boolean to print pod information + - boolean to print rootfs size + - boolean to print oci runtime and container state + +**Append the following lines to your function:** + +```Go + // Container list + var latestContainers = 1 + containerLatestList, err := containers.List(connText, nil, nil, &latestContainers, nil, nil, nil) + if err != nil { + fmt.Println(err) + os.Exit(1) + } + fmt.Printf("Latest container is %s\n", containerLatestList[0].Names[0]) +``` + +**Run it:** + +```bash +$ go run main.go +Welcome to the Podman Go bindings tutorial +Pulling Busybox image... +Pulling Fedora image... +Listing images... +[docker.io/library/busybox:latest registry.fedoraproject.org/fedora:latest] +Starting Fedora container... +Latest container is dazzling_mclean +$ +``` + + +### Inspect Container <a name="inspect-container"></a> +Containers can be inspected using the containers.Inspect() binding. +containers.Inspect() takes 3 arguments: + - context + - image name or ID + - optional boolean to check for container size + + +**Append the following lines to your function:** + +```Go + // Container inspect + ctrData, err := containers.Inspect(connText, r.ID, nil) + if err != nil { + fmt.Println(err) + os.Exit(1) + } + fmt.Printf("Container uses image %s\n", ctrData.ImageName) + fmt.Printf("Container running status is %s\n", ctrData.State.Status) +``` + +**Run it:** + +```bash +$ go run main.go +Welcome to the Podman Go bindings tutorial +Pulling Busybox image... +Pulling Fedora image... +Listing images... +[docker.io/library/busybox:latest registry.fedoraproject.org/fedora:latest] +Starting Fedora container... +Latest container is peaceful_noether +Fedora Container uses image registry.fedoraproject.org/fedora:latest +Fedora Container running status is running +$ +``` + + +### Stop Container <a name="stop-container"></a> + +A container can be stopped by the containers.Stop() binding. +containers.Stop() takes 3 arguments: + - context + - image name or ID + - optional timeout + +**Append the following lines to your function:** + +```Go + // Container stop + fmt.Println("Stopping the container...") + err = containers.Stop(connText, r.ID, nil) + if err != nil { + fmt.Println(err) + os.Exit(1) + } + ctrData, err = containers.Inspect(connText, r.ID, nil) + if err != nil { + fmt.Println(err) + os.Exit(1) + } + fmt.Printf("Container running status is now %s\n", ctrData.State.Status) +``` + +**Run it:** + +```bash +$ go run main.go +Welcome to the Podman Go bindings tutorial +Pulling Busybox image... +Pulling Fedora image... +Listing images... +[docker.io/library/busybox:latest registry.fedoraproject.org/fedora:latest] +Starting Fedora container... +Latest container is peaceful_noether +Fedora Container uses image registry.fedoraproject.org/fedora:latest +Fedora Container running status is running +Stopping Fedora container... +Container running status is now exited +``` + + +### Debugging tips <a name="debugging-tips"></a> + +To debug in a development setup, you can start the Podman system service +in debug mode like so: + +```bash +$ podman --log-level=debug system service -t 0 +``` + +The `--log-level=debug` echoes all the logged requests and is useful to +trace the execution path at a finer granularity. A snippet of a sample run looks like: + +```bash +INFO[0000] podman filtering at log level debug +DEBU[0000] Called service.PersistentPreRunE(podman --log-level=debug system service -t0) +DEBU[0000] Ignoring libpod.conf EventsLogger setting "/home/lsm5/.config/containers/containers.conf". Use "journald" if you want to change this setting and remove libpod.conf files. +DEBU[0000] Reading configuration file "/usr/share/containers/containers.conf" +DEBU[0000] Merged system config "/usr/share/containers/containers.conf": {Editors note: the remainder of this line was removed due to Jekyll formatting errors.} +DEBU[0000] Using conmon: "/usr/bin/conmon" +DEBU[0000] Initializing boltdb state at /home/lsm5/.local/share/containers/storage/libpod/bolt_state.db +DEBU[0000] Overriding run root "/run/user/1000/containers" with "/run/user/1000" from database +DEBU[0000] Using graph driver overlay +DEBU[0000] Using graph root /home/lsm5/.local/share/containers/storage +DEBU[0000] Using run root /run/user/1000 +DEBU[0000] Using static dir /home/lsm5/.local/share/containers/storage/libpod +DEBU[0000] Using tmp dir /run/user/1000/libpod/tmp +DEBU[0000] Using volume path /home/lsm5/.local/share/containers/storage/volumes +DEBU[0000] Set libpod namespace to "" +DEBU[0000] Not configuring container store +DEBU[0000] Initializing event backend file +DEBU[0000] using runtime "/usr/bin/runc" +DEBU[0000] using runtime "/usr/bin/crun" +WARN[0000] Error initializing configured OCI runtime kata: no valid executable found for OCI runtime kata: invalid argument +DEBU[0000] using runtime "/usr/bin/crun" +INFO[0000] Setting parallel job count to 25 +INFO[0000] podman filtering at log level debug +DEBU[0000] Called service.PersistentPreRunE(podman --log-level=debug system service -t0) +DEBU[0000] Ignoring libpod.conf EventsLogger setting "/home/lsm5/.config/containers/containers.conf". Use "journald" if you want to change this setting and remove libpod.conf files. +DEBU[0000] Reading configuration file "/usr/share/containers/containers.conf" +``` + +If the Podman system service has been started via systemd socket activation, +you can view the logs using journalctl. The logs after a sample run look like so: + +```bash +$ journalctl --user --no-pager -u podman.socket +-- Reboot -- +Jul 22 13:50:40 nagato.nanadai.me systemd[1048]: Listening on Podman API Socket. +$ +``` + +```bash +$ journalctl --user --no-pager -u podman.service +Jul 22 13:50:53 nagato.nanadai.me systemd[1048]: Starting Podman API Service... +Jul 22 13:50:54 nagato.nanadai.me podman[1527]: time="2020-07-22T13:50:54-04:00" level=error msg="Error refreshing volume 38480630a8bdaa3e1a0ebd34c94038591b0d7ad994b37be5b4f2072bb6ef0879: error acquiring lock 0 for volume 38480630a8bdaa3e1a0ebd34c94038591b0d7ad994b37be5b4f2072bb6ef0879: file exists" +Jul 22 13:50:54 nagato.nanadai.me podman[1527]: time="2020-07-22T13:50:54-04:00" level=error msg="Error refreshing volume 47d410af4d762a0cc456a89e58f759937146fa3be32b5e95a698a1d4069f4024: error acquiring lock 0 for volume 47d410af4d762a0cc456a89e58f759937146fa3be32b5e95a698a1d4069f4024: file exists" +Jul 22 13:50:54 nagato.nanadai.me podman[1527]: time="2020-07-22T13:50:54-04:00" level=error msg="Error refreshing volume 86e73f082e344dad38c8792fb86b2017c4f133f2a8db87f239d1d28a78cf0868: error acquiring lock 0 for volume 86e73f082e344dad38c8792fb86b2017c4f133f2a8db87f239d1d28a78cf0868: file exists" +Jul 22 13:50:54 nagato.nanadai.me podman[1527]: time="2020-07-22T13:50:54-04:00" level=error msg="Error refreshing volume 9a16ea764be490a5563e384d9074ab0495e4d9119be380c664037d6cf1215631: error acquiring lock 0 for volume 9a16ea764be490a5563e384d9074ab0495e4d9119be380c664037d6cf1215631: file exists" +Jul 22 13:50:54 nagato.nanadai.me podman[1527]: time="2020-07-22T13:50:54-04:00" level=error msg="Error refreshing volume bfd6b2a97217f8655add13e0ad3f6b8e1c79bc1519b7a1e15361a107ccf57fc0: error acquiring lock 0 for volume bfd6b2a97217f8655add13e0ad3f6b8e1c79bc1519b7a1e15361a107ccf57fc0: file exists" +Jul 22 13:50:54 nagato.nanadai.me podman[1527]: time="2020-07-22T13:50:54-04:00" level=error msg="Error refreshing volume f9b9f630982452ebcbed24bd229b142fbeecd5d4c85791fca440b21d56fef563: error acquiring lock 0 for volume f9b9f630982452ebcbed24bd229b142fbeecd5d4c85791fca440b21d56fef563: file exists" +Jul 22 13:50:54 nagato.nanadai.me podman[1527]: Trying to pull registry.fedoraproject.org/fedora:latest... +Jul 22 13:50:55 nagato.nanadai.me podman[1527]: Getting image source signatures +Jul 22 13:50:55 nagato.nanadai.me podman[1527]: Copying blob sha256:dd9f43919ba05f05d4f783c31e83e5e776c4f5d29dd72b9ec5056b9576c10053 +Jul 22 13:50:55 nagato.nanadai.me podman[1527]: Copying config sha256:00ff39a8bf19f810a7e641f7eb3ddc47635913a19c4996debd91fafb6b379069 +Jul 22 13:50:55 nagato.nanadai.me podman[1527]: Writing manifest to image destination +Jul 22 13:50:55 nagato.nanadai.me podman[1527]: Storing signatures +Jul 22 13:50:55 nagato.nanadai.me systemd[1048]: podman.service: unit configures an IP firewall, but not running as root. +Jul 22 13:50:55 nagato.nanadai.me systemd[1048]: (This warning is only shown for the first unit using IP firewalling.) +Jul 22 13:51:15 nagato.nanadai.me systemd[1048]: podman.service: Succeeded. +Jul 22 13:51:15 nagato.nanadai.me systemd[1048]: Finished Podman API Service. +Jul 22 13:51:15 nagato.nanadai.me systemd[1048]: podman.service: Consumed 1.339s CPU time. +$ +``` + + +## Wrap Up +Podman v2 provides a set of Go bindings to allow developers to integrate Podman +functionality conveniently in their Go application. These Go bindings require +the Podman system service to be running in the background and this can easily +be achieved using systemd socket activation. Once set up, you are able to use a +set of Go based bindings to create, maintain and monitor your container images, +containers and pods in a way which fits very nicely in many production environments. + + +## References +- Podman v2 is available for most major distributions along with MacOS and Windows. +Installation details are available on the [Podman official website](https://podman.io/getting-started/). + +- Documentation can be found at the [Podman Docs page](https://docs.podman.io). +It also includes a section on the [RESTful API](https://docs.podman.io/en/latest/Reference.html). |