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Re: Configuration approach recommendations



Hello Jon,

We considered using services instead of processes and found that they also
have disadvantage. The problem with the services approach is in the UI.
Consider the following example:

User configures node group to run MapReduce workers, i.e. TaskTrackers
processes. It does not matter if he creates a Node Group Template, or edits
Node Group during cluster creation, since the UI will be similar in both
cases. Since properties are categorized by services, user is asked to fill
in all the parameters for that service (MapReduce) including those for
JobTracker like “JobTracker heap size”, etc. As a result user has to dig
through many irrelevant options during configuration, which is very bad. I
think we should not blindly copy files configuration even if users got used
to it. We are making a web console and we should use the advantages it
provides over editing files. I.e. if we can filter out irrelevant options
for user, then why not do it? That does not change configuration flow much,
but at the same time it is much more convenient for a user.

As for Templates, our intention is to provide all users with ability to
create their own templates, both for Cluster and Node Group. In fact we see
no reason to reject a user have his own templates. We just _think_ that
users will prefer administrators or more experienced users to prepare
templates for them, because these people should be better at Hadoop cluster

Right now the main concern we have is timing. We already spent much time
designing phase 2 and I believe that our initial design evolved into
something much better. But we think that it is about time to freeze specs
we have for phase 2 and start implementing them. At the same time we can
have a background conversation on how we can improve the design in phase 3.
We believe that it will not be hard to change this part specifically.

The solution for the problem we see is to unify processes and services
categorization. Config object can have the following 2-dimensional


   applicable_target = <process name> | <service name> | “general”

   scope = “node” | “cluster”


<process name> = “process:tasktracker” | “process:jobtracker” |
“process:datanode” | …

<service name> = “service:mapreduce” | “service:hdfs” | …

Here is a table example parameters for various combinations of target/scope:




Don’t use this combination, use Service/Cluster instead

JobTracker heap size, mapred.tasktracker.map.tasks.maximum


dfs.replication, mapred.output.compression.type



user SSL key for cluster machines

OS parameters like ulimits

Again, as I said we propose to do this only after we complete Pluggable
Provisioning Mechanism and make sure it is working. Right now we suggest to
implement our old proposal with with processes, just to avoid further
changes in design in this phase.



2013/5/22 Jon Maron <jmaron@xxxxxxxxxxxxxxx>

> We still have some concerns regarding the current configuration approach.
>  I'd like to highlight two major issues:
> 1)  Component level configuration - Configuring at the component level is
> contrary to the Hadoop configuration approach which is structured around
> host level configuration (as opposed to component level).  Trying to
> configure at the component level runs contrary to that configuration
> philosophy and would likely be questioned by Hadoop users.  In addition,
> this approach can be rather error prone.  For example, consider a
> deployment in which the name node and secondary name node are hosted on the
> same server (a not uncommon approach).  Both components obviously share a
> great deal of configuration properties.  If a user is leveraging the UI and
> is configuring these items at the component level he/she will:
> - repeat the configuration for each component, a process that may be
> rather frustrating
> - will have no idea which of the settings will actually be leveraged since
> there is essentially a race condition here - the properties potentially end
> up in the same configuration file on the given node group, so which of the
> properties actually win?
> 2)  There doesn't appear to be a facility for making changes that span
> node groups.  The cluster templates are essentially immutable - they are
> created by an admin and are not seen as modifiable via the UI by users (at
> least as far as we can tell).  The other configuration alternative
> currently is to configure the specific node groups.  So, for example, how
> do I approach the task of modifying 3 HDFS properties across all 10 node
> groups I've defined?  It seems that with the current approach I will have
> to repeatedly make the same modifications to each node group in turn?
> We believe both of these issues can be remedied by modifying the
> configuration approach to be more service centric rather than component
> centric.  While the cluster template still provides for global, immutable
> settings, allowing users to configure at the service level will allow for
> global changes across node groups.  We still want to address the node group
> level configuration (host level overrides), so perhaps the config structure
> could be redesigned as follows:
> *config*
> Describes a single config parameter.
> name
> description
> type
> Type could be string, integer, enum, array of [int, string]
> default_value
> is_optional
> * service - a service name or "GENERAL"*
> *
> *
> To be clear about what the service attribute values mean:
> *service name* - this property value is a service-based property that is
> valid at to be applied to the service across a cluster or to a specific
> node group (i.e. the property can be applied to all instances of the
> service across the cluster or to a specific set of hosts in a node group).
>  The scope is determined by where the user selected the property value (the
> node group interface or the cluster interface) and specified in the
> user_input "scope" attribute (see below)
> *"GENERAL"* - this property value is not specific to a hadoop service.
>  It can be specified at the cluster or node group level as well.
> * *
> In the UI, the interfaces can provide the setting of all values.  The UI
> can categorize the properties based on service etc to present to the user.
>  If the user is in a node group configuration panel, the configuration
> settings will be scoped to the node group.  If they are in a cluster
> template or the like, the property value should be scoped to the entire
> cluster.
> The user_input object remains unchanged.  User input values assigned to
> the cluster_configs attribute of the Cluster object are cluster scope
> properties (GENERAL or service based).  User input values associated to the
> embedded node groups (node_configs attribute within a particular node_group
> in node_groups list  of the cluster object) are associated to the specific
> node group (GENERAL or service based).
> Again, we feel that this aligns the interface much more closely with the
> way users interact with Hadoop.  The attempt to align configuration with
> specific service components is somewhat contrived and introduces an
> impedance mismatch that users will probably reject.
> --
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