Task dependency is probably too vague to discuss specifically. Mesos currently does not explicitly support arbitrary task dependencies. You mentioned colocation, one type of dependency, so let's look at it.
If I understood you correctly, you would like to colocate a task from framework B to the same node where a task from framework A is running. The first problem is to get a list of such nodes (and keep them updated, because task may crash, migrate and so on). This can be done, say, by using Mesos DNS or alike. The second problem is to ensure that framework gets enough resources from that nodes. A possible solution here is to put both frameworks A and B into the same role and use dynamic reservations to ensure enough resources are laid away for both tasks. Disadvantages: you should know about all dependencies upfront, frameworks should be in the same role. Now the question is, why would you need to colocate workloads? I would say this is something you should avoid if possible, like any extra constraint that complicate the system. Probably the only 100% legitimate use case for colocation is data locality. Solving this particular problem seems easier than to address arbitrary task dependencies. If all you try to achieve is making sure a specific service represented by a framework X is running and ready in the cluster, you can do that by running specific checks before starting a depending framework Y or launching a new task in this framework. If your question is about whether Y should know about X and know how to check readiness of X in the cluster, I'd say you'd better keep that abstracted: Y scheduler can accept a rule how to check readiness on startup. On Wed, Dec 14, 2016 at 5:14 AM, haosdent <[email protected]> wrote: > Hi, @Petr. > > > Like if I want to run my task collocated with some other tasks on the > same node I have to make this decision somewhere. > Do you mean "POD" here? > > For my cases, if there are some dependencies between my tasks, I use > database, message queue or zookeeper to implement my requirement. > > On Wed, Dec 14, 2016 at 3:09 AM, Petr Novak <[email protected]> wrote: > >> Hello, >> >> I want to execute tasks which requires some other tasks from other >> framework(s) already running. I’m thinking where such logic/strategy/policy >> belongs in principle. I understand scheduling as a process to decide where >> to execute task according to some resources availability, typically CPU, >> mem, net, hdd etc. >> >> >> >> If my task require other tasks running could I generalize and consider >> that those tasks from other frameworks are kind of required resources and >> put this logic/strategy decisions into scheduler? Like if I want to run my >> task collocated with some other tasks on the same node I have to make this >> decision somewhere. >> >> >> >> Does it make any sense? I’m asking because I have never thought about >> other frameworks/tasks as “resources” so that I could put them into >> scheduler to satisfy my understanding of a scheduler. Or it rather belongs >> higher like to a framework, or lower to an executor? Should scheduler be >> dedicated to decisions about resources which are offered and am I mixing >> concepts? >> >> >> >> Or I just should keep distinction between resources and >> requirements/policies or whatever but anyway does this kind of logic still >> belongs to scheduler or it should be somewhere else? I’m trying to >> understand which logic should be in scheduler and what should go somewhere >> else. >> >> >> >> Many thanks, >> >> Petr >> >> >> > > > > -- > Best Regards, > Haosdent Huang >
