In a distributed setup, how do I programatically start containers?
More specifically, does there exist any API similar to deploying and undeploying streams for setting up and tearing down containers?
There is currently no way to do this via an API. Containers are only known to the cluster after they are started. Upon initialization, the container registers itself with ZooKeeper. Running a container requires XD to be installed on that host which is currently a manual process: download,unzip,configure, as is starting the container. Some automation of operations will likely be provided in a future release.
Related
Currently we have Java applications deployed in an Application server (Websphere to be exact). To fix common performance and memory related problems we encounter, we do tweakings like:
Adjust the thread pool setting - to prevent waiting threads.
Adjust the application server's garbage collection behavior.
Now, there is a plan to move them to containers (via Docker and using Spring Boot). So essentially they would be converted to Spring boot apps running on Docker containers. Now my question is, what is the equivalent of doing #1 and #2 in this kind of setup? is there still a way to adjust thread pool and garbage collection? or is it a different way now? or this shouldn't be an issue because docker swarm can manage all this and scale?
Edit: for the meantime, docker swarm will be used for managing containers. Kubernetes is still not in the picture.
According to the documentation:
An application is considered ready as soon as application and
command-line runners have been called, see Spring Boot application
lifecycle and related Application Events.
So it doesn't seem to be considering external systems suchs a database. Is this correct?
How could we make the ReadinessStateHealthIndicator evaluate the state of such systems so the pod is taken away from the k8s service load balancer when they are failing of are not available?
I have a java application running on a single Instance EC2 server. I want to implement autoscaling in the server, but my java application will not work on active-active mode.
So, I have started looking at Hazelcast IMDG open source for Application Scaling Purpose.
I am new to Hazelcast. So, Can anyone give me the idea about How can I implement Hazelcast open source for my Application Scaling and what will be the steps?
You can deploy a Hazelcast cluster on EC2 with Auto Scaling turned on. See here for details: https://github.com/hazelcast/hazelcast-aws/blob/master/README.md
I have two docker instances that I launch with docker-compose.
One holds a Cassandra instance
One holds a Spring Boot application that tries to connect to that application.
However, the Spring Boot application will always fail, because it's trying to connect to a Cassandra instance that is not ready yet to take connections.
I have tried:
Using restart:always in Docker-compose
This still doesn't always work, because the Cassandra might be up 'enough' to no longer crash the Spring Boot application, but not up 'enough' to have successfully created the Table/Column family. On top of that, this is a very hacky solution.
Using healthcheck
It seems like healthcheck in compose doesn't have restart capabilities
Using a bash script as entrypoint
In the hope that I could use netstat,ping,... whatever to determine that readiness state of Cassandra
Right now the only thing that really works is using that same bash script and sleep the process for x seconds, then start the jar. This is even more hacky...
Does anyone have an idea on how to solve this?
Thanks!
Does the spring boot service defined in the docker-compose.yml depends_on the cassandara service? If yes then the service is started only if the cassandra service is ready.
https://docs.docker.com/compose/compose-file/#depends_on
Take a look at this github repository, to find a healthcheck for the cassandra service.
https://github.com/docker-library/healthcheck
CONCLUSION
After some discussion we found out that docker-compose seems not to provide a functionality for waiting until services are up and healthy, such as Kubernetes and Openshift provide (See comments below). They recommend to use wrapper script (docker-entrypoint.sh) which waits for the depending service to come up, which make binaries necessary, the actual service shouldn't use such as the cassandra client binary. Additionally the service depending on cassandra could never get up if cassandra doesn't, which shouldn't happen.
A main thing with microservices is that they have to be resilient for failures and are not supposed to die or not to come up if a depending service is currently not available or unexpectedly disappears. Therefore the microservice should be implemented in a way so that it retries to get connection after startup or an unexpected disappearance. Unexpected is a word actually wrongly used in this context, because you should always expect such issues in a distributed environment, and even with docker-compose you will face issues like that as discussed in this topic.
The following link points to a tutorial which helped to integrate cassandra properly into a spring boot application. It provides a way to implement the retrieval of a cassandra connection with a retry behavior, therefore the service is resilient to a non existing cassandra database and will not fail to start anymore. Hope this helps others as well.
https://dzone.com/articles/containerising-a-spring-data-cassandra-application
I am working on Spring XD and GemFire XD. I want to understand how Spring XD's distributed environment works. I know spring xd uses either redis or rabittmq as the transport.
I am clear about this, I have install spring xd and rabittmq on one machine. I changed the redis.properties file and added hostnames.
Do I need to install spring xd on all the machines? If so, after installing, how to bring those up.
On the master machine, I will do ./xd-admin and ./xd-container
How do you start up the nodes (spring xd instances/workers) so that they can listen for instructions from xd-admin?
Please help me on this.
Thanks,
-Suyodhan
Redis is used for analytics as only supported platform. For transport, you need either Redis or Rabbit.
Basically you just need to install Redis and RabbitMQ per their respective documentation. They can be in same or different servers, Ideally you would use their high availability option. For example Redis Sentinal. YOu don't need RabbitMQ unless you want to change the default transport from Redis to Rabbit. Once you install Redis and Rabbit, bring them up and provide their host:port info (and any additional as applicable) to the servers.yml in XD install (in all nodes) and bring up admin and containers. Evrything should work automatically by using zookeeper as the means to manage the distributed runtime.
If you use Spring XD in distributed mode, I assume you have set up zookeeper as well. (If not check this http://docs.spring.io/spring-xd/docs/1.0.0.M7/reference/html/#_setting_up_zookeeper )
Admin and Container instances register themselves with Zookeeper as they come up. Admin queries zookeeper for available containers and assign tasks like deploying modules. Zookeeper is the trick behind Distributed mode.
Hope this helps.
You will install Spring xd one time on one machine, Spring XD will be connected to your hdfs distributed scaled out environment.
You need to start the followings:
1. redis or rappitMQ in your case
2. hsqldb server
3. container
4. admin
when you start spring xd, you need to register the name node firstly using the command:
hadoop config fs --name hdfs://serverip:8020
then you can use any module defined in spring xd (using stream or batch) by specifying its parameters directly without specifying those in the server.yml file.
Moha.