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3.1 Introduction
This is the HTCondor Administrator's Manual.
Its purpose is to aid in
the installation and administration of an HTCondor pool. For help on
using HTCondor, see the HTCondor User's Manual.
An HTCondor pool
is comprised of a single machine which serves as the
central manager,
and an arbitrary number of other machines that
have joined the pool. Conceptually, the pool is a collection of
resources (machines) and resource requests (jobs). The role of HTCondor
is to match waiting requests with available resources. Every part of
HTCondor sends periodic updates to the central manager, the centralized
repository of information about the state of the pool. Periodically,
the central manager assesses the current state of the pool and tries
to match pending requests with the appropriate resources.
Each resource has an owner,
the one who sets the policy for the use of the machine. This
person has absolute power over the use of the machine,
and HTCondor goes out
of its way to minimize the impact on this owner caused by HTCondor. It
is up to the resource owner to define a policy for when HTCondor
requests will
serviced and when they will be denied.
Each resource request has an owner as well: the
user who submitted the job. These people want HTCondor to provide as
many CPU cycles as possible for their work. Often the interests of
the resource owners are in conflict with the interests of the resource
requesters.
The job of the HTCondor administrator is to configure the HTCondor pool to
find the happy medium that keeps both resource owners and users of
resources satisfied. The purpose of this manual is to relate
the mechanisms that HTCondor provides to enable the administrator to find
this happy medium.
3.1.1 The Different Roles a Machine Can Play
Every machine in an HTCondor pool can serve a variety of roles. Most
machines serve more than one role simultaneously. Certain roles can
only be performed by a single machine in the pool. The following list
describes what these roles are and what resources are required on the
machine that is providing that service:
- Central Manager
- There can be only one central manager for the pool.
This machine is the collector of information, and the negotiator
between resources and resource requests. These two halves of the
central manager's responsibility are performed by separate daemons, so
it would be possible to have different machines providing those two
services. However, normally they both live on the same machine. This
machine plays a very important part in the HTCondor pool and should be
reliable. If this machine crashes, no further matchmaking can be
performed within the HTCondor system,
although all current matches remain in effect until they are broken
by either party involved in the match.
Therefore, choose for central manager
a machine that is likely to be up and running all the time,
or at least one that will be rebooted quickly if something goes wrong.
The central manager will
ideally have a good network connection to all the
machines in the pool, since these pool machines all send updates over
the network to the central manager.
- Execute
- Any machine in the pool,
including the central manager,
can be configured as to whether or not it should execute HTCondor jobs.
Obviously, some of the machines will have to serve this
function, or the pool will not be useful.
Being an execute machine does not require lots of resources.
About the only resource that might matter is disk space.
In general the
more resources a machine has in terms of swap space, memory, number of CPUs,
the larger variety of resource requests it can serve.
- Submit
- Any machine in the pool,
including the central manager,
can be configured as to whether or not it should allow HTCondor
jobs to be submitted.
The resource requirements for a submit machine
are actually much greater than the resource requirements for an
execute machine. First, every submitted job that is
currently running on a remote machine runs a process on
the submit machine.
As a result, lots of running jobs
will need a fair amount of swap space and/or real memory.
In addition,
the checkpoint files from standard universe jobs are stored on
the local disk of the submit machine.
If these jobs have a large
memory image and there are a lot of them,
the submit machine will need a lot of disk space to hold these files.
This disk space requirement can be
somewhat alleviated by using a checkpoint server,
however the binaries of the jobs are still stored on the submit machine.
- Checkpoint Server
- Machines in the pool can be configured to act as
checkpoint servers.
This is optional, and is not part of the
standard HTCondor binary distribution. A checkpoint server is a
machine that stores checkpoint files for sets of jobs.
A machine with this role should have lots of disk space
and a good network connection to the rest of the pool, as the traffic
can be quite heavy.
3.1.2 The HTCondor Daemons
The following list describes all the daemons and programs that could
be started under HTCondor and what they do:
- condor_master
- This daemon
is responsible for keeping all the
rest of the HTCondor daemons running on each machine in the pool. It
spawns the other daemons, and it periodically checks to see if there are
new binaries installed for any of them. If there are, the
condor_master daemon will
restart the affected daemons. In addition, if any daemon crashes, the
condor_master will send e-mail to the HTCondor administrator of the pool and
restart the daemon. The condor_master also supports various
administrative commands that enable the administrator to start,
stop or reconfigure daemons remotely.
The condor_master will run on every machine in
the pool, regardless of the functions that each machine is performing.
- condor_startd
- This daemon
represents a given resource to the HTCondor pool,
as a machine capable of running jobs.
It advertises certain attributes about machine that are used to
match it with pending resource requests.
The condor_startd will run on any
machine in the pool that is to be able to execute jobs.
It is responsible for enforcing the policy that the resource owner configures,
which determines under what conditions jobs will be started,
suspended, resumed, vacated, or killed.
When the condor_startd is ready to
execute an HTCondor job, it spawns the condor_starter.
- condor_starter
- This daemon
is the entity that actually
spawns the HTCondor job on a given machine. It sets up the
execution environment and monitors the job once it is running. When a
job completes, the condor_starter notices this, sends back any status
information to the submitting machine, and exits.
- condor_schedd
- This daemon
represents resource requests to
the HTCondor pool. Any machine that is to be a submit machine
needs to have a condor_schedd running.
When users submit jobs,
the jobs go to the condor_schedd, where they are stored in the
job queue.
The condor_schedd manages the job queue.
Various tools to view and
manipulate the job queue,
such as condor_submit, condor_q, and condor_rm,
all must connect to the condor_schedd to do their work. If the
condor_schedd is not running on a given machine,
none of these commands will work.
The condor_schedd advertises the number of waiting jobs in its job queue and
is responsible for claiming available resources to serve those requests.
Once a job has been matched with a given resource, the
condor_schedd spawns a condor_shadow daemon to serve that
particular request.
- condor_shadow
- This daemon
runs on the machine where a given
request was submitted and acts as the resource manager for the
request. Jobs that are linked for HTCondor's standard universe, which
perform remote system calls, do so via the condor_shadow. Any
system call performed on the remote execute machine is sent over the
network, back to the condor_shadow which performs the
system call on the submit machine, and the result
is sent back over the network to the job on the execute machine.
In addition,
the condor_shadow is responsible for making decisions about the request,
such as where checkpoint files should be stored,
and how certain files should be accessed.
- condor_collector
- This daemon
is responsible for collecting
all the information about the status of an HTCondor pool. All other
daemons periodically send ClassAd updates to
the condor_collector. These ClassAds contain all the information about the
state of the daemons, the resources they represent or resource
requests in the pool.
The condor_status command can be used to query the
condor_collector for specific information about various parts of HTCondor.
In addition, the HTCondor daemons themselves query the condor_collector for
important information, such as what address to use for sending
commands to a remote machine.
- condor_negotiator
- This daemon
is responsible for all the match making within the HTCondor system.
Periodically, the condor_negotiator
begins a negotiation cycle, where it queries the
condor_collector for
the current state of all the resources in the pool. It contacts each
condor_schedd that has waiting resource requests in priority order,
and tries to match available resources with those requests.
The condor_negotiator is
responsible for enforcing user priorities in the system, where the
more resources a given user has claimed, the less priority they have
to acquire more resources. If a user with a better priority has jobs
that are waiting to run, and resources are claimed by a user with a
worse priority, the condor_negotiator can preempt that resource and match it
with the user with better priority.
NOTE: A higher numerical value of the user priority in HTCondor
translate into worse priority for that user. The best priority
is 0.5, the lowest numerical value, and this priority gets
worse as this number grows.
- condor_kbdd
- This daemon
is used on both Linux and Windows platforms.
On those platforms, the condor_startd frequently cannot determine
console (keyboard or mouse) activity directly from the system, and
requires a separate process to do so.
On Linux, the
condor_kbdd connects to the X Server and periodically checks to see
if there has been any activity.
On Windows, the condor_kbdd runs as the logged-in user and registers
with the system to receive keyboard and mouse events.
When it detects console activity, the condor_kbdd sends a
command to the condor_startd.
That way, the condor_startd knows the machine owner
is using the machine again and can perform whatever actions are
necessary, given the policy it has been configured to enforce.
- condor_ckpt_server
- The checkpoint server
services requests to store and retrieve checkpoint files.
If the pool is configured to use a checkpoint server,
but that machine or the server itself is down,
HTCondor will revert to sending the checkpoint
files for a given job back to the submit machine.
- condor_gridmanager
- This daemon
handles management and execution of all grid
universe jobs.
The condor_schedd invokes the condor_gridmanager when
there are grid universe jobs in the queue,
and the condor_gridmanager exits when there are no more
grid universe jobs in the queue.
- condor_credd
- This daemon
runs on Windows platforms to manage password storage in a secure manner.
- condor_had
- This daemon
implements the high availability of a pool's central manager
through monitoring the communication of necessary daemons.
If the current, functioning, central manager machine
stops working, then this daemon ensures that another
machine takes its place, and becomes the central manager of
the pool.
- condor_replication
- This daemon
assists the condor_had daemon by keeping an updated copy of the
pool's state. This state provides a better transition
from one machine to the next, in the event
that the central manager machine stops working.
- condor_transferer
- This short lived daemon is invoked by
the condor_replication daemon to accomplish the task of transferring
a state file before exiting.
- condor_procd
- This daemon
controls and monitors process families within HTCondor. Its use
is optional in general, but it must be used if
group-ID based tracking (see Section 3.14.11) is enabled.
- condor_job_router
- This daemon
transforms vanilla universe jobs into grid
universe jobs, such that the transformed jobs are capable
of running elsewhere, as appropriate.
- condor_lease_manager
- This daemon
manages leases in a persistent manner.
Leases are represented by ClassAds.
- condor_rooster
- This daemon wakes hibernating machines based
upon configuration details.
- condor_defrag
- This daemon manages the draining of machines
with fragmented partitionable slots, so that they become available
for jobs requiring a whole machine or larger fraction of a machine.
- condor_shared_port
- This daemon listens for incoming TCP packets
on behalf of HTCondor daemons, thereby reducing the number of required
ports that must be opened when HTCondor is accessible through a firewall.
When compiled from source code,
the following daemons may be compiled in to provide optional functionality.
- condor_hdfs
- This daemon manages the configuration of a
Hadoop file system as well as the invocation of a properly configured
Hadoop file system.
Next: 3.2 Installation, Start Up,
Up: 3. Administrators' Manual
Previous: 3. Administrators' Manual
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