When starting up Enterprise Neo4j in HA the 1st server is starting as the master.
I have a requirement where I want to control who the master is in the cluster, is that actually possible in Neo4j?
What would happen if I set all the slaves with 'ha.slave_coordinator_update_mode=none'. Will this permit me to have a single master, and if it goes down no other instance will become the master, and when that instance recovers will become the master again.
Or, if I didn't use that setting, the master goes down and a slave takes over, when the original master comes back up will it just act as a slave or will it become the master again?
Is there some configuration that will permit control of that, the documentation doesn't cover that very clearly.
Orlok,
You can use ha.slave_only to ensure an instance doesn't ever become master. See http://docs.neo4j.org/chunked/stable/ha-configuration.html
That effectively allows you to add as many read slaves as you wish, but beware that you lose high availability if you only have one instance that can become master. I.e. have a few instances master-ready, setup with ha.slave_only=false, as well as a bunch of read slaves.
Regards,
Lasse
Related
I have a Jenkins master and two agents. However the connectivity to one agent(agentA) is bit shaky and I want to use the other agent(agentB) when the connectivity to the first one is not available.
I am only using the Jenkins web interface and have not used scripts. I am trying to figure out how it can be done using the "Restrict where this project can be run" option in job's configuration. I tried using agentA|| agentB but when agentA is not available it hangs saying "pending - agentA is offline"
Is it possible to have a configuration to achieve what I need?
I can;t leave it blank because I have other agent (agentC, agentD) which do not want this job to run in.
I am not an admin of the Jenkins server, hence adding new plugins is not my preferred option but it can be done.
As noted in Least Load plugin,
By default Jenkins tries to allocate a jobs to the last node is was executed on. This can result in nodes being left idle while other nodes are overloaded.
As you generalized the example, I'm not 100% sure if your situation can be solved by simply better labelling of your nodes or you want to look at least load plugin (it is designed for balancing the load across nodes). Your example appears to show Node names (ie; agentA/agentB). The Queue allocation logic may be "Only A or Only B", then Jenkins sticks to it. Load balancing may not address that as while a Node (a Computer) name is also a label, it may have additional logic tied to it.
If you label the pair of nodes in a pool with a common label, say "CapabilityA", and constrain your jobs to run where "CapabilityA" rather than the node names, you may find jobs float across the pool (to B if A is not available. That's how we have our nodes labelled - by Capability, and we see jobs floating across nodes, but only once the first node is full (4 executors each), so not balanced.
Nodes can have many labels and you can use label conditions to have complex constraints.
I've just read through Neo4j's tutorial on creating a cluster (link at bottom), but no information is given regarding which node is designated as the 'master', or how this is done.
Let's say I'm working with the first example, where there are a total of three nodes installed on three separate machines. How would I make one the master?
If any part of my question is mistaken, please let me know and I will be quick to edit.
Here's that link:
neo4j manual
As far as I can read in the documentation, you can only set a master in advance if all other nodes in the cluster have the ha.slave_only property set to true. However I would advise not to do this as your cluster needs at least one other non-slave_only node to elect as new master in case the elected master goes down.
Identifying the master can be done via the HA REST endpoints. You can find all the info at http://neo4j.com/docs/stable/ha-rest-info.html
The docs of Neo4j state that when running in HA mode, you get eventual consistency. This is a quote from that page:
All updates will however propagate from the master to other slaves
eventually so a write from one slave may not be immediately visible on
all other slaves
My question is: is there a configuration that will allow me to write a cluster with strong consistency, of course at the cost of reduced performance? I'm looking for some sort of active-passive failover cluster configuration.
There is such an config option. ha.tx_push_factor determines to how many slaves a transaction should be pushed to synchronously. When setting this to ha.tx_push_factor=<clustersize>-1 you have immediate full consistency.
I've installed a master jenkins instance and 2 slave nodes.
Both slaves are not synchronous with the master. Sometimes it shows that the slaves are 2 days or 1 hour in the future, sometimes it shows that time on slaves is behind the master - it seems to randomize.
Because of this some selenium tests or builds or other jobs doesn't work correctly anymore. The problem occurred suddenly and it doesn't matter which version of jenkins has been installed.
Has anyone an idea how to fix this problem?
Thank you very much.
Cheers
Christoph
It is hard to explain why the time difference would vary abruptly between the two machines. I assume you are referring to the information given by the http://jenkins.mydomain/computer/ url.
Normally you want to keep your machines in time sync, and enable NTP clients on each host, each pointing to the same set of NTP servers, either internal to your organization (if that is available), or the standard free NTP services available on the web.
Do you have this setup already and see abrupt time variations? If so, review your list of NTP services and make sure to use reliable ones and also the same list, it should help. Maybe narrow it down to just one service and then expand if need be.
I would like to setup the jenkins build farm in such a way that the fail over of all nodes are handled including the master. I am not able to find an answer for the question "what if master node goes down?".
I need a hot-hot setup where in if one node goes down the other should be able to pick up the queue and when both are up, they should process the jobs exclusively. Can we setup two nodes where each node is master and slave to each other? Does that create a serious conflict?
I am new to Jenkins distributed build setup and your help is much appreciated.
Thanks!
There is the CloudBees Jenkins Enterprise product http://jenkins-enterprise.cloudbees.com/docs/user-guide-bundle/ha-sect-failover.html which is able to deal with a master failure. That is a commercial product but if High Availability is a requirement then it could be worth the price.