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Full example interaction

Important: this tutorial is out of date and does not match the latest API. It will be updated soon.

  1. Make sure that the rbd and overlay modules are loaded:

    modprobe rbd overlay

  2. Start the imageapi-server service. We'll just run it by hand:

    $ nohup sudo ./imageapi-server --port 8080 --scheme http &

    This starts and backgrounds the service on 127.0.0.1:8080 . This is insecure, but good for testing.

  3. Attach an RBD object. We will attach one named systemd.sqsh that already contains a systemd based image in a squashfs filesystem.

    $ curl -s -XPOST -H 'Content-Type: application/json' -d '{"monitors":["192.168.1.48"],"pool":"rbd","image":"systemd.sqsh","options":{"ro":true,"name":"admin","secret":"XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"}}' http://localhost:8080/imageapi/v1/attach/rbd | jq
{
  "image": "systemd.sqsh",
  "monitors": [
    "192.168.1.48"
  ],
  "options": {
    "name": "admin",
    "ro": true,
    "secret": "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
  },
  "pool": "rbd"
}

    We have successfully attached the RBD object (read-only). We can see this with:

    $ dmesg | tail -n3
[ 9584.859653] libceph: mon0 (1)192.168.1.48:6789 session established
[ 9584.861001] libceph: client124116 fsid 4bc8e219-dd58-473f-ac79-c947bd1c4d41
[ 9584.905617] rbd: rbd0: capacity 10737418240 features 0x1
$ ls -l /dev/rbd0
brw-rw---- 1 root disk 253, 0 Feb 10 23:53 /dev/rbd0

  4. Now that we have attached the object, we need to mount it.

    $ curl -s -XPOST -H 'Content-type: application/json' -d '{"id": 0, "fs_type": "squashfs", "mount_options": [ "ro" ] }' http://localhost:8080/imageapi/v1/mount/rbd | jq
{
  "fs_type": "squashfs",
  "id": 0,
  "mount_options": [
    "ro"
  ],
  "mountpoint": "/var/run/imageapi/mounts/mount_746184320"
}

    We see that the image got mounted under /var/run/imageapi/mounts/mount_746184320.

    $ sudo ls /var/run/imageapi/mounts/mount_746184320
bin  boot  dev	etc  home  lib	lib64  media  mnt  opt	proc  root  run  sbin  srv  sys  tmp  usr  var

  5. To make make a non-destructive, locally read-write image, we mount an overlay over this image.

    $ curl -s -XPOST -H 'Content-type: application/json' -d '{ "lower": [ 0 ]}' http://localhost:8080/imageapi/v1/mount/overlay | jq
{
  "id": 1,
  "lower": [
    0
  ],
  "mountpoint": "/var/run/imageapi/mounts/mount_725692383",
  "upperdir": "/var/run/imageapi/mounts/upper_014522290",
  "workdir": "/var/run/imageapi/mounts/work_400792425"
}

    Note that the "lower" array referenced the rbd mount "id" from above. We can handle multiple overlay layers by adding more entries to this list.

    The mountpoint at /var/run/imageapi/mounts/mount_725692383 is read-write.

  6. Now we can define our container on this mount:

    $ curl -s -XPOST -H 'Content-type: application/json' -d '{ "name": "test-container", "mount": { "id": 1, "kind": "overlay" }, "command": "/usr/lib/systemd/systemd", "state": "created", "systemd": true }' http://localhost:8080/imageapi/v1/container | jq
{
  "command": "/usr/lib/systemd/systemd",
  "logfile": "/var/run/imageapi/logs/0-1613002114.log",
  "mount": {
    "id": 1,
    "kind": "overlay"
  },
  "name": "test-container",
  "namespaces": null,
  "state": "created",
  "systemd": true
}

    The mount structure specified using an overlay mount of id: 1 that we just created. command specifies the entrypoint command, in this case, systemd. If we're running systemd some extra container setup is necessary. The "systemd": true option makes sure that happens.

    Note, namespaces is currently unused. All containers get mount, pid, uts, and ipc namespaces by default.

    We see a reference to a log file for this container. Currently it's pretty boring:

    $ sudo cat /var/run/imageapi/logs/0-1613002114.log
2021/02/11 00:08:34 container(0): container created

    That's because we didn't request that the container actually start. We could have with "state": "running".

  7. Since we didn't auto-start our container, let's start it:

    $ curl -s -XGET http://localhost:8080/imageapi/v1/container/0/running | jq
{
  "command": "/usr/lib/systemd/systemd",
  "logfile": "/var/run/imageapi/logs/0-1613002114.log",
  "mount": {
    "id": 1,
    "kind": "overlay"
  },
  "name": "test-container",
  "namespaces": null,
  "state": "running",
  "systemd": true
}

    We can ps to see the processes running.

    $ ps -elF --forest
...
4 S root        1074    1010  0  80   0 - 88261 -       7756   0 21:36 pts/0    00:00:00  |           \_ sudo ./imageapi-server --scheme=http --port=8080
4 S root        1075    1074  0  80   0 - 178813 -     23640   0 21:36 pts/0    00:00:00  |               \_ ./imageapi-server --scheme=http --port=8080
4 S root        1534    1075  2  80   0 - 24282 -      13004   0 21:44 ?        00:00:00  |                   \_ /usr/lib/systemd/systemd
4 S root        1563    1534  0  80   0 -  7761 -      10572   0 21:44 ?        00:00:00  |                       \_ /usr/lib/systemd/systemd-journald
4 S root        1610    1534  0  80   0 -  5176 -       9408   1 21:44 ?        00:00:00  |                       \_ /usr/lib/systemd/systemd-logind
...

    We can use nsenter to "enter" the container:

    $ sudo nsenter -t 1534 -a bash
[root@kraken /]# ps waux
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root           1  0.5  0.4 170732 12604 ?        Ss   00:14   0:00 /usr/lib/systemd/systemd
root          30  0.0  0.5  41236 12832 ?        Ss   00:14   0:00 /usr/lib/systemd/systemd-journald
root          73  0.0  0.4 248184 11180 ?        Ss   00:14   0:00 /usr/sbin/sssd -i --logger=files
root         103  0.0  0.5 251732 12928 ?        S    00:14   0:00 /usr/libexec/sssd/sssd_be --domain implicit_files --uid 0 --gid 0 --logger=files
root         109  0.0  1.5 274916 38160 ?        S    00:14   0:00 /usr/libexec/sssd/sssd_nss --uid 0 --gid 0 --logger=files
root         170  0.2  0.3  20704  9576 ?        Ss   00:16   0:00 /usr/lib/systemd/systemd-logind
root         194  0.3  0.1 231648  4200 ?        S    00:16   0:00 bash
root         206  0.0  0.1 234240  3760 ?        R+   00:16   0:00 ps waux

    We can check our currently running containers:

    $ curl -s http://localhost:8080/imageapi/v1/container | jq
[
  {
    "command": "/usr/lib/systemd/systemd",
    "logfile": "/var/run/imageapi/logs/0-1613002114.log",
    "name": "test-container",
    "mount": {
      "id": 1,
      "kind": "overlay"
    },
    "namespaces": null,
    "state": "running",
    "systemd": true
  }
]

  8. Notice that we passed a "name" parameter to our container. This parameter is optional, but can be useful. If and only if a name is provided, containers can be accessed by name. These calls have the same structure as access by id, but have byname in the path. For instance, the following will stop the container:

    $ curl -s http://localhost:8080/imageapi/v1/container/byname/test-container/exited | jq
[
  {
    "command": "/usr/lib/systemd/systemd",
    "logfile": "/var/run/imageapi/logs/0-1613002114.log",
    "name": "test-container",
    "mount": {
      "id": 1,
      "kind": "overlay"
    },
    "namespaces": null,
    "state": "stopping",
    "systemd": true
  }
]

  9. Finally, let's tear it all down:

$ curl -XDELETE http://localhost:8080/imageapi/v1/container/0
$ curl -XDELETE http://localhost:8080/imageapi/v1/mount/overlay/1
$ curl -XDELETE http://localhost:8080/imageapi/v1/mount/rbd/0
$ curl -XDELETE http://localhost:8080/imageapi/v1/attach/rbd/0
$ sudo cat /var/run/imageapi/logs/0-1613002114.log
2021/02/11 00:08:34 container(0): container created
2021/02/11 00:14:54 container(0): starting container
2021/02/11 00:14:54 container(0): validating image
2021/02/11 00:14:54 container(0): validating init
2021/02/11 00:14:54 init: making all mounts private
2021/02/11 00:14:54 init: preparing image
2021/02/11 00:14:54 init: mounting /proc
2021/02/11 00:14:54 init: mounting /dev
2021/02/11 00:14:54 init: mounting /dev/shm
2021/02/11 00:14:54 init: mounting /dev/mqueue
2021/02/11 00:14:54 init: mounting /dev/pts
2021/02/11 00:14:54 init: mounting /sys
2021/02/11 00:14:54 init: mounting /run
2021/02/11 00:14:54 init: mounting /tmp
2021/02/11 00:14:54 init: mounting /sys/fs/cgroup
2021/02/11 00:14:54 init: mounting /var/lib/journal
2021/02/11 00:14:54 init: making device file /dev/null
2021/02/11 00:14:54 init: making device file /dev/zero
2021/02/11 00:14:54 init: making device file /dev/full
2021/02/11 00:14:54 init: making device file /dev/tty
2021/02/11 00:14:54 init: making device file /dev/random
2021/02/11 00:14:54 init: making device file /dev/urandom
2021/02/11 00:14:54 init: creating symlink /dev/pts/ptmx -> /dev/ptmx
2021/02/11 00:14:54 init: creating symlink /proc/self/fd -> /dev/fd
2021/02/11 00:14:54 init: creating symlink /proc/self/fd/0 -> /dev/stdin
2021/02/11 00:14:54 init: creating symlink /proc/self/fd/1 -> /dev/stdout
2021/02/11 00:14:54 init: creating symlink /proc/self/fd/2 -> /dev/stderr
2021/02/11 00:14:54 init: executing init
2021/02/11 00:20:07 container(0): container deleted
$ ls -l /dev/rbd0
ls: cannot access '/dev/rbd0': No such file or directory

Note: The ImageAPI will refuse to deleted a running resouce, so you'll want to request the exited state, and wait for stopping to complete before issuing -XDELETE on a container, for instance.

  1. Ok, so that was fun... but what if we want to define everything at once?

The ImageAPI supports (as of v0.1.0) the ability to definte nested resources. For instance, you could define an overaly that includes an underlying RBD with:

{
 "lower": [
   {
     "kind": "rbd",
     "rbd": {
       "fs_type": "squashfs",
       "mount_options": [
         "ro"
       ],
       "rbd": {
         "monitors": [
           "192.168.1.48"
         ],
         "pool": "rbd",
         "image": "systemd.sqsh",
         "options": {
           "ro": true,
           "name": "admin",
           "secret": "XXX"
         }
       }
     }
   }
 ]
}

More inteteresting is a container comletely specified with mounts and attachments:

The following posted to /imageapi/v1/container would attach an RBD, mount it, mount an overalay, define a container on top of it, and run that container in a single definition:

{
  "mount": {
    "kind": "overlay",
    "overlay": {
      "lower": [
        {
          "kind": "rbd",
          "rbd": {
            "fs_type": "squashfs",
            "mount_options": [
              "ro"
            ],
            "rbd": {
              "monitors": [
                "192.168.1.48"
              ],
              "pool": "rbd",
              "image": "systemd.sqsh",
              "options": {
                "ro": true,
                "name": "admin",
                "secret": "AQC71s9fOrv9KxAAmH7vB3vQGyVmwbBd005B4A=="
              }
            }
          }
        }
      ]
    }
  },
  "command": "/usr/lib/systemd/systemd",
  "systemd" true,
  "name": "systemd.sqsh",
  "state": "running"
}

Because this container is named, it could be exited with a single call to /imageapi/v1/container/byname/systemd.sqsh/exited, and then deleted. The ImageAPI will track refererences to any object (RBD, mount, ...) and will regularly garbage collect any unused resources, so if you delete this container, the ImageAPI will automatically unmount the overlay, unmount the squashfs, and unmap the RBD. If the resources were created through a nested call like this, deleting the top-level resource will delete all references to the next level down, which will lead to its garbage collection. This will cascade until all resources are collected.