I'm using Mesos and Marathon. I created an application on Marathon.
When applications failover to other node in cluster, can we control where they should invoke?
I tried with LIKE "Constrains" in Marathon but it doesn't work as my expectation.
Thanks in advance
You can use a LIKE or UNLIKE constraint (or set of contraints) to restrict where marathon can place any given app instance; however, you can't choose a specific one upon failure.
Related
I have two servers in a HA mode. I'd like to know if is it possible to deploy an application on the slave server? If yes, how to configure it in jgroups? I need to run a specific program that access the master database, but I would not like to run on master serve to avoid overhead on it.
JGroups itself does not know much about WildFly and the deployments, it only creates a communication channel between nodes. I don't know where you get the notion of master/slave, but JGroups always has single* node marked as coordinator. You can check the membership through Channel.getView().
However, you still need to deploy the app on both nodes and just make it inactive if this is not its target node.
*) If there's no split-brain partition, or similar rare/temporal issues
How to deploy apache airflow (formally known as airbnb's airflow) scheduler in high availability?
I am not asking about the backend DB or RabbitMQ that should obviously be deployed in high availability configuration.
My main focus is the scheduler - is there something special needs to be done?
After a bit digging I found that it is not safe to run multiple schedulers simoultanously, this means that out of the box - airflow schedulers are not safe to use in high availablity environments.
The airflow team are planning to solve this issue by adding a lock mechanism on the DAG data structure, but this is not implemented yet (I checked by running 2 schedulers and saw that they schedule the same dag instances which is not good).
This is described here:
https://groups.google.com/forum/#!topic/airbnb_airflow/-1wKa3OcwME
I did found a way to workaround this high availalbilty issue by wrapping the schedulers with my own code and use cluster tools for leader election (I personanlly use consul for this purpose). This way only the elected master is running the scheduler and when the master is down the slave replaces him.
Please consider this when u use airflow in high availabilty environments since out of the box, airflow scheduler is currently not suitable for this (unless you solve this issue yourself).
Edit - an alternative approach to the master slave solution is to use a cluster manager/scheduler to make sure that only one airflow scheduler instance is always available. This approach relies on the self healing abilities of the cluster manager u have. For example both mesos and nomad supports this kind of configuration (I presonally chose nomad for its simplicity).
My personal experience was to follow the instructions I found for some best practices; that is to restart the scheduler every 10 runs ( -N 10 ) and use this software when possible:
https://github.com/teamclairvoyant/airflow-scheduler-failover-controller
I also use a DAG which pings a monitoring system to be sure that the scheduler has not gone away.
In my scenario, I have 2 schedulers (on 2 separate docker swarms), with the standby cluster scheduler turned off (using docker swarm service scale=0). I needed to make sure the primary scheduler had stopped fully before I started up the standby scheduler. What I found was that having 2 running schedulers (even for a brief time period) resulted in an occasional DAG scheduled to run on both clusters leading to duplicate reports generated from two different cluster zone.
I have a cluster setup with nodes that are not reliable and can go down (They are aws spot instances). I am trying to make sure that my application master only launches on the reliable nodes (aws on demand instances) of the cluster. Is there a workaround for the same? My cluster is being managed by hortonworks ambari.
This can be achieved by using node labels. I was able to use the property in spark spark.yarn.am.nodeLabelExpression to restrict my application master to a set of nodes while running spark on yarn. Add the node labels to whichever nodes you want to use for application masters.
I have cluster of 3 Mesos slaves, where I have two applications: “redis” and “memcached”. Where redis depends on memcached and the requirement is both of the applications/services should start on same node instead of different slave nodes.
So I have created the application group and added the dependency properly in the JSON file. After launching the JSON file via “v2/groups” REST API, I observe that sometime both application group will start on same node but sometimes it will start on different slaves which breaks our requirement.
So intent/requirement is; if any application fails to start on a slave both the application should failover to other slave node. Also can I configure the JSON file to tell Marathon to start the application group on slave-1 (specific slave first) if it is available else start it on other slave in a cluster. Due to some reason if this application group will start on other slave can Marathon relaunch the application group to slave-1 if it is available to serve the request.
Thanks in advance for help.
Edit/Update (2):
Mesos, Marathon, and DC/OS support for PODs is available now:
DC/OS: https://dcos.io/docs/1.9/usage/pods/using-pods/
Mesos: https://github.com/apache/mesos/blob/master/docs/nested-container-and-task-group.md
Marathon: https://github.com/mesosphere/marathon/blob/master/docs/docs/pods.md
I assume you are talking about marathon apps.
Marathon application groups don't have any semantics concerning co-location on the same node and the same is the case for dependencies.
You seem to be looking for a Kubernetes like Pod abstraction in marathon, which is on the roadmap but not yet available (see update above :-)).
Hope this helps!
I think this should be possible (as a workaround) if you specify the correct app contraints within the group's JSON.
Have a look at the example request at
https://mesosphere.github.io/marathon/docs/generated/api.html#v2_groups_post
and the constraints syntax at
https://mesosphere.github.io/marathon/docs/constraints.html
e.g.
"constraints": [["hostname", "CLUSTER", "slave-1"]]
should do. Downside is that there will be no automatic failover to another slave that way. Still, I'd be curious why both apps need to specifically run on the same slave node...
I didn't find info whether it is possible to define something like an Event-hook upon up/down-scaling or deletion of an App in the Marathon Rest API docs at https://mesosphere.github.io/marathon/docs/rest-api.html
What I'd like to achieve is that I'm able to backup some data from a running Docker container before be is destroyed. For example, I run a cluster of Elasticsearch nodes on Marathon, and I would like to delay the deletion of the app until the then triggered "Create snapshot to external disk resource" process is finished.
Is there currently something I could use?
Marathon provides an Event Bus covering some phases of the lifecycle. Beyond that, currently the only other option I see is to go for Mesos Modules/Hooks.