Commit 2f2f1289 authored by Iustin Pop's avatar Iustin Pop
Browse files

Remove 'Detailed Design' from design-2.2.rst

This also bumps up the rest of the headings.
Signed-off-by: default avatarIustin Pop <>
Reviewed-by: default avatarGuido Trotter <>
parent 227e546f
......@@ -11,24 +11,22 @@ adding new features and improvements over 2.1, in a timely fashion.
.. contents:: :depth: 4
Detailed design
As for 2.1 we divide the 2.2 design into three areas:
- core changes, which affect the master daemon/job queue/locking or
all/most logical units
- logical unit/feature changes
- external interface changes (eg. command line, os api, hooks, ...)
- external interface changes (e.g. command line, OS API, hooks, ...)
Core changes
Master Daemon Scaling improvements
Current state and shortcomings
Currently the Ganeti master daemon is based on four sets of threads:
......@@ -50,7 +48,7 @@ Also, with the current architecture, masterd suffers from quite a few
scalability issues:
Core daemon connection handling
Since the 16 client worker threads handle one connection each, it's very
easy to exhaust them, by just connecting to masterd 16 times and not
......@@ -60,7 +58,7 @@ with better handling long running operations making sure the client is
informed that everything is proceeding, and doesn't need to time out.
Wait for job change
The REQ_WAIT_FOR_JOB_CHANGE luxi operation makes the relevant client
thread block on its job for a relative long time. This is another easy
......@@ -69,7 +67,7 @@ time out, moreover this operation is negative for the job queue lock
contention (see below).
Job Queue lock
The job queue lock is quite heavily contended, and certain easily
reproducible workloads show that's it's very easy to put masterd in
......@@ -120,7 +118,7 @@ To increase the pain:
remote rpcs to complete (starting, finishing, and submitting jobs)
Proposed changes
In order to be able to interact with the master daemon even when it's
under heavy load, and to make it simpler to add core functionality
......@@ -135,7 +133,7 @@ smaller in number of threads, and memory size, and thus also easier to
understand, debug, and scale.
Connection handling
We'll move the main thread of ganeti-masterd to asyncore, so that it can
share the mainloop code with all other Ganeti daemons. Then all luxi
......@@ -148,7 +146,7 @@ serializing the reply, which can then be sent asynchronously by the main
thread on the socket.
Wait for job change
The REQ_WAIT_FOR_JOB_CHANGE luxi request is changed to be
subscription-based, so that the executing thread doesn't have to be
......@@ -173,7 +171,7 @@ Other features to look at, when implementing this code are:
them at a maximum rate (lower priority).
Job Queue lock
In order to decrease the job queue lock contention, we will change the
code paths in the following ways, initially:
......@@ -202,10 +200,10 @@ its benefits.
Remote procedure call timeouts
Current state and shortcomings
The current RPC protocol used by Ganeti is based on HTTP. Every request
consists of an HTTP PUT request (e.g. ``PUT /hooks_runner HTTP/1.0``)
......@@ -230,10 +228,10 @@ use application-level timeouts because these cover both machine down and
unresponsive node daemon cases.
Proposed changes
RPC glossary
Function call ID
Unique identifier returned by ``ganeti-noded`` after invoking a
......@@ -242,7 +240,7 @@ Function process
Process started by ``ganeti-noded`` to call actual (backend) function.
Initially we chose HTTP as our RPC protocol because there were existing
libraries, which, unfortunately, turned out to miss important features
......@@ -273,7 +271,7 @@ Inter-node RPC calls would no longer be blocking indefinitely and there
would be an implicit ping-mechanism.
Request handling
To support the protocol changes described above, the way the node daemon
handles request will have to change. Instead of forking and handling
......@@ -345,10 +343,10 @@ function processes and wait for all of them to terminate.
Inter-cluster instance moves
Current state and shortcomings
With the current design of Ganeti, moving whole instances between
different clusters involves a lot of manual work. There are several ways
......@@ -359,10 +357,10 @@ necessary in the new environment. The goal is to improve and automate
this process in Ganeti 2.2.
Proposed changes
Authorization, Authentication and Security
Until now, each Ganeti cluster was a self-contained entity and wouldn't
talk to other Ganeti clusters. Nodes within clusters only had to trust
......@@ -424,7 +422,7 @@ equivalent to the source cluster and must verify the server's
certificate while providing a client certificate to the server.
Copying data
To simplify the implementation, we decided to operate at a block-device
level only, allowing us to easily support non-DRBD instance moves.
......@@ -442,7 +440,7 @@ consumption, everything is read from the disk and sent over the network
directly, where it'll be written to the new block device directly again.
#. Third party tells source cluster to shut down instance, asks for the
instance specification and for the public part of an encryption key
......@@ -510,7 +508,7 @@ Workflow
#. Source cluster removes the instance if requested
Instance move in pseudo code
.. highlight:: python
......@@ -651,7 +649,7 @@ clusters and what happens on both clusters.
.. highlight:: text
Miscellaneous notes
- A very similar system could also be used for instance exports within
the same cluster. Currently OpenSSH is being used, but could be
......@@ -679,10 +677,10 @@ Miscellaneous notes
Privilege separation
Current state and shortcomings
All Ganeti daemons are run under the user root. This is not ideal from a
security perspective as for possible exploitation of any daemon the user
......@@ -694,7 +692,7 @@ side effects, like letting the user run some ``gnt-*`` commands if one
is in the same group.
For Ganeti 2.2 the implementation will be focused on a the RAPI daemon
only. This involves changes to ```` so it's possible to drop
......@@ -710,13 +708,13 @@ and then drop privileges before contacting the master daemon.
Feature changes
KVM Security
Current state and shortcomings
Currently all kvm processes run as root. Taking ownership of the
hypervisor process, from inside a virtual machine, would mean a full
......@@ -725,7 +723,7 @@ authentication secrets, full access to all running instances, and the
option of subverting other basic services on the cluster (eg: ssh).
Proposed changes
We would like to decrease the surface of attack available if an
hypervisor is compromised. We can do so adding different features to
......@@ -734,7 +732,7 @@ possibilities, in the absence of a local privilege escalation attack, to
subvert the node.
Dropping privileges in kvm to a single user (easy)
By passing the ``-runas`` option to kvm, we can make it drop privileges.
The user can be chosen by an hypervisor parameter, so that each instance
......@@ -761,7 +759,7 @@ But the following would remain an option:
- read unprotected data on the node filesystem
Running kvm in a chroot (slightly harder)
By passing the ``-chroot`` option to kvm, we can restrict the kvm
process in its own (possibly empty) root directory. We need to set this
......@@ -784,7 +782,7 @@ It would still be possible though to:
Running kvm with a pool of users (slightly harder)
If rather than passing a single user as an hypervisor parameter, we have
a pool of useable ones, we can dynamically choose a free one to use and
......@@ -795,7 +793,7 @@ This would mean interfering between machines would be impossible, and
can still be combined with the chroot benefits.
Running iptables rules to limit network interaction (easy)
These don't need to be handled by Ganeti, but we can ship examples. If
the users used to run VMs would be blocked from sending some or all
......@@ -808,7 +806,7 @@ we can properly apply, without limiting the instance legitimate traffic.
Running kvm inside a container (even harder)
Recent linux kernels support different process namespaces through
control groups. PIDs, users, filesystems and even network interfaces can
......@@ -820,7 +818,7 @@ interface, thus reducing performance, so we may want to avoid that, and
just rely on iptables.
Implementation plan
We will first implement dropping privileges for kvm processes as a
single user, and most probably backport it to 2.1. Then we'll ship
......@@ -833,11 +831,11 @@ slip after the 2.2 release.
External interface changes
The OS variants implementation in Ganeti 2.1 didn't prove to be useful
enough to alleviate the need to hack around the Ganeti API in order to
......@@ -856,7 +854,7 @@ These changes to the OS API will bump the API version to 20.
OS version
A new ``os_version`` file will be supported by Ganeti. This file is not
required, but if existing, its contents will be checked for consistency
......@@ -870,14 +868,14 @@ import/export scripts must increase the version, since they break
intra-cluster migration.
The interface between Ganeti and the OS scripts will be based on
environment variables, and as such the parameters and their values will
need to be valid in this context.
The parameter names will be declared in a new file, ``parameters.list``,
together with a one-line documentation (whitespace-separated). Example::
......@@ -896,7 +894,7 @@ line interface in lowercased form; as such, there shouldn't be any two
parameters which differ in case only.
The values of the parameters are, from Ganeti's point of view,
completely freeform. If a given parameter has, from the OS' point of
......@@ -917,7 +915,7 @@ the value space).
Environment variables
The parameters will be exposed in the environment upper-case and
prefixed with the string ``OSP_``. For example, a parameter declared in
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