The containerd client is very chatty at the best of times. Because the
libcontained API is stateless and references containers and processes by
string ID for every method call, the implementation is essentially
forced to use the containerd client in a way which amplifies the number
of redundant RPCs invoked to perform any operation. The libcontainerd
remote implementation has to reload the containerd container, task
and/or process metadata for nearly every operation. This in turn
amplifies the number of context switches between dockerd and containerd
to perform any container operation or handle a containerd event,
increasing the load on the system which could otherwise be allocated to
workloads.
Overhaul the libcontainerd interface to reduce the impedance mismatch
with the containerd client so that the containerd client can be used
more efficiently. Split the API out into container, task and process
interfaces which the consumer is expected to retain so that
libcontainerd can retain state---especially the analogous containerd
client objects---without having to manage any state-store inside the
libcontainerd client.
Signed-off-by: Cory Snider <csnider@mirantis.com>
Since commit e9b9e4ace2 has landed, there is a chance that
container.RWLayer is nil (due to some half-removed container). Let's
check the pointer before use to avoid any potential nil pointer
dereferences, resulting in a daemon crash.
Note that even without the abovementioned commit, it's better to perform
an extra check (even it's totally redundant) rather than to have a
possibility of a daemon crash. In other words, better be safe than
sorry.
[v2: add a test case for daemon.getInspectData]
[v3: add a check for container.Dead and a special error for the case]
Fixes: e9b9e4ace2
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Cory Snider