• David Johnson's avatar
    Docker server-side core, esp new libimageops support for Docker images. · 66366489
    David Johnson authored
    The docker VM server-side goo is mostly identical to Xen, with slightly
    different handling for parent images.  We also support loading external
    Docker images (i.e. those without a real imageid in our DB; in that
    case, user has to set a specific stub image, and some extra per-vnode
    metadata (a URI that points to a Docker registry/image repo/tag);
    the Docker clientside handles the rest.
    
    Emulab Docker images map to a Emulab imageid:version pretty seamlessly.
    For instance, the Emulab `emulab-ops/docker-foo-bar:1` image would map
    to `<local-registry-URI>/emulab-ops/emulab-ops/docker-foo-bar:1`; the
    mapping is `<local-registry-URI>/pid/gid/imagename:version`.  Docker
    repository names are lowercase-only, so we handle that for the user; but
    I would prefer that users use lowercase Emulab imagenames for all Docker
    images; that will help us.  That is not enforced in the code; it will
    appear in the documentation, and we'll see.
    
    Full Docker imaging relies on several other libraries
    (https://gitlab.flux.utah.edu/emulab/pydockerauth,
    https://gitlab.flux.utah.edu/emulab/docker-registry-py).  Each
    Emulab-based cluster must currently run its own private registry to
    support image loading/capture (note however that if capture is
    unnecessary, users can use the external images path instead).  The
    pydockerauth library is a JWT token server that runs out of boss's
    Apache and implements authn/authz for the per-Emulab Docker registry
    (probably running on ops, but could be anywhere) that stores images and
    arbitrates upload/download access.  For instance, nodes in an experiment
    securely pull images using their pid/eid eventkey; and the pydockerauth
    emulab authz module knows what images the node is allowed to pull
    (i.e. sched_reloads, the current image the node is running, etc).  Real
    users can also pull images via user/pass, or bogus user/pass + Emulab
    SSL cert.  GENI credential-based authn/z was way too much work, sadly.
    There are other auth/z paths (i.e. for admins, temp tokens for secure
    operations) as well.
    
    As far as Docker image distribution in the federation, we use the same
    model as for regular ndz images.  Remote images are pulled in to the
    local cluster's Docker registry on-demand from their source cluster via
    admin token auth (note that all clusters in the federation have
    read-only access to the entire registries of any other cluster in the
    federation, so they can pull images).  Emulab imageid handling is the
    same as the existing ndz case.  For instance, image versions are lazily
    imported, on-demand; local version numbers may not match the remote
    image source cluster's version numbers.  This will potentially be a
    bigger problem in the Docker universe; Docker users expect to be able to
    reference any image version at any time anywhere.  But that is of course
    handleable with some ex post facto synchronization flag day, at least
    for the Docker images.
    
    The big new thing supporting native Docker image usage is the guts of a
    refactor of the utils/image* scripts into a new library, libimageops;
    this is necessary to support Docker images, which are stored in their
    own registry using their own custom protocols, so not amenable to our
    file-based storage.  Note: the utils/image* scripts currently call out
    to libimageops *only if* the image format is docker; all other images
    continue on the old paths in utils/image*, which all still remain
    intact, or minorly-changed to support libimageops.
    
    libimageops->New is the factory-style mechanism to get a libimageops
    that works for your image format or node type.  Once you have a
    libimageops instance, you can invoke normal image logical operations
    (CreateImage, ImageValidate, ImageRelease, et al).  I didn't do every
    single operation (for instance, I haven't yet dealt with image_import
    beyond essentially generalizing DownLoadImage by image format).
    Finally, each libimageops is stateless; another design would have been
    some statefulness for more complicated operations.   You will see that
    CreateImage, for instance, is written in a helper-subclass style that
    blurs some statefulness; however, it was the best match for the existing
    body of code.  We can revisit that later if the current argument-passing
    convention isn't loved.
    
    There are a couple outstanding issues.  Part of the security model here
    is that some utils/image* scripts are setuid, so direct libimageops
    library calls are not possible from a non-setuid context for some
    operations.  This is non-trivial to resolve, and might not be worthwhile
    to resolve any time soon.  Also, some of the scripts write meaningful,
    traditional content to stdout/stderr, and this creates a tension for
    direct library calls that is not entirely resolved yet.  Not hard, just
    only partly resolved.
    
    Note that tbsetup/libimageops_ndz.pm.in is still incomplete; it needs
    imagevalidate support.  Thus, I have not even featurized this yet; I
    will get to that as I have cycles.
    66366489
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