master-slave

I am wondering if, using C (or C++ or Rust) and javascript, I am able to do CRUD operations to a shared data object. Using the most basic example, here would be an example or each of the operations:

I have AMQ Artemis cluster, shared-store HA (master-slave), 2.17.0.

I noticed that all my clusters (active servers only) that are idle (no one is using them) using from 10% to 20% of CPU, except one, which is using around 1% (totally normal). I started investigating...

Long story short - only one cluster has a completely normal CPU usage. The only difference I've managed to find that if I connect to that normal cluster's master node and attempt telnet slave 61616 - it will show as connected. If I do the same in any other cluster (that has high CPU usage) - it will show as rejected.

In order to better understand what is happening, I enabled DEBUG logs in instance/etc/logging.properties. Here is what master node is spamming:

I have setup two ActiveMQ Artemis brokers (version 2.17) on a master-slave configuration with a shared file system for HA. During testing with heavy traffic I would stop master broker and see that the slave takes over and starts forwarding messages to consumers. After a while I can witness that a number of messages seem to have been stuck in queues. The "stuck" messages are considered as "in delivery" as I can see from the Artemis UI when queried.

My issue is that even when I restart the master broker these messages are not delivered to the consumer and remain stuck even if more messages are still populating the same queue and the queue has consumers. My assumption was that it had to do with previous connections setup by consumers still remaining active because there were not acknowledged.

So I did try to setup on broker, or on client connection string (tcp://host1:61616,tcp://host2:61616)?ha=true&connectionTtl=60000&reconnectAttempts=-1) but that did not seemed to have any effect since the connection would not be closed and the messages were not released. For consuming messages I am using Artemis JMS Spring client with a CachingConnectionFactory but also tried JmsPoolConnectionFactory to no avail.

I have been using Windows 10 operating system. I want to use slony master-slave setup with postgresql. For this, I have downloaded enterprise database 13.1 version. After installation I select slony download from stackbuilder plus. Then I copied these 2 files to offline windows 10 machine. I install both of them. After that, i try to run a simple slonik script to setup master. while executing "init cluster" command i get file not found error, c:servershare/slony1_base.2.8.sql. Do you have an idea for the solution?

I have two DB servers and I am trying to make a Master-Slave replication for my PostgreSQL with TimescaleDB extension.

I went through this process:

1. [Both] Install PostgreSQL 12 on CentOS 7.

2. [Both] Initialize DB and install TimescaleDB. (followed official website tutorial)

3. [Both] Do all the firewall-cmd, postgresql.conf, and pg_hba.conf works.

4. [Master] Create initial database.

5. [Slave] stop PostgreSQL, remove everything in /var/lib/pgsql/12/data, and pg_basebackup from Master.

   (Command I used: pg_basebackup -h [MASTER_DB_IP] -D /var/lib/pgsql/12/data -U [REP_USER] -vP -W)

6. [Slave] set hot_standby = on and create recovery.conf

7. [Slave] start PostgreSQL to check replication works.

8. [Slave] This error occurs and cannot start PostgreSQL.

My question is built on the question and answers from this question - What's the difference between ClusterIP, NodePort and LoadBalancer service types in Kubernetes?

The question might not be well-formed for some of you.

I am trying to understand the differences between clusterIP, nodePort and Loadbalancer and when to use these with an example. I suppose that my understanding of the following concept is correct K8s consists of the following components

• Node - A VM or physical machine. Runs kubectl and docker process
• Pod - unit which encapsulates container(s) and volumes (storage). If a pod contains multiple containers then shared volume could be the way for process communication
• Node can have one or multiple pods. Each pod will have its own IP
• Cluster - replicas of a Node. Each node in a cluster will contain same pods (instances, type)

Here is the scenario:

My application has a web server (always returning 200OK) and a database (always returning the same value) for simplicity. Also, say I am on GCP and I make images of webserver and of the database. Each of these will be run in their own respective pods and will have 2 replicas.

I suppose I'll have two clusters (cluster-webserver (node1-web (containing pod1-web), node2-web (containing pod2-web)) and cluster-database (node1-db (containing pod1-db), node2-db (containing pod2-db)). Each node will have its own ip address (node1-webip, node2-webip, node1-dbip, node2-dbip)

A client application (browser) should be able to access the web application from outside web cluster but the database shouldn't be accessible from outside database cluster. However web nodes should be able to access database nodes)

• Question 1 - Am I correct that if I create a service for web (webServiceName) and a service for database then by default, I'll get only clusterIP and a port (or targetPort).
• Question 1.2 - Am I correct that clusterIP is an IP assigned to a pod, not the node i.e. in my example, clusterIP gets assigned to pod1-web, not node1-web even though node1 has only pod1.
• Question 1.3 - Am I correct that as cluster IP is accessible from only within the cluster, pod1-web and pod2-web can talk to each other and pod1-db and pod2-db can talk to each other using clusterIP/dns:port or clusterIP/dns:targetPort but web can't talk to database (and vice versa) and external client can't talk to web? Also, the nodes are not accessible using the cluster IP.
• Question 1.4 - Am I correct that dns i.e. servicename.namespace.svc.cluster.local would map the clusterIP?
• Question 1.5 - For which type of applications I might use only clusterIP? Where multiple instances of an application need to communicate with each other (eg master-slave configuration)?

If I use nodePort then K8s will open a port on each of the node and will forward nodeIP/nodePort to cluster IP (on pod)/Cluster Port

• Question 2 - Can web nodes now access database nodes using nodeIP:nodePort which will route the traffic to database's clusterIP (on pod):clusterport/targertPort? ( I have read that clusterIP/dns:nodePort will not work).
• Question 2.1 - How do I get a node's IP? Is nodeIP the IP I'll get when I run describe pods command?
• Question 2.2 - Is there a dns equivalent for the node IP as node IP could change during failovers. Or does dns now resolve to the node's IP instead of clusterIP?
• Question 2.3 - I read that K8s will create endpoints for each service. Is endpoint same as node or is it same as pod? If I run kubectl describe pods or kubectl get endpoints, would I get same IPs)?

As I am on GCP, I can use Loadbalancer for web cluster to get an external IP. Using the external IP, the client application can access the web service

I saw this configuration for a LoadBalancer

I'm trying to setup simple redis configuration with only 2 services: master and slave.

Here's part of my .gitlab-ci.yml with master-slave setup:

I had have to redefine the description of the problem.

I have PostgreSQL cloud-based database, making 1.5M requests per day. I checked the statistics of the individual queries themselves with different variants of the extracted data. In general, the individual queries seem to be okay (they are really simple and are unlikely to delay). The problem occurs while the application is running. The application is an internet game. During one gaming session, new records (with the current state of the game) are constantly being written to the database. A lot of inserts are made at this time. The user may wish to see the history of the game at any time(while such inserts are in progress). At this point, when the writing-service is adding new records into the database, the reading-service reads the data. Such reading is very rare compared to writing, it occurs in a ratio of 1:100 (but such reading will occur more often in the future). Service ugh-read usually reads data in 0-6 seconds. Sometimes the reading time increases to over 40 or even 100 seconds. Rare jumps like 10-20 seconds would be acceptable, but I absolutely need to get rid of jumps over 40 seconds. For this particular problem I think about replication MASTER-SLAVE (write_only-read_only)

The additional information: commentator asked about:

• Cloud service: gcp
• Service limit: limits: memory: 1500Mi cpu: 500m
• Postgres version: 10

If would be good, I could present the structure of queries and tables. Everything is written in spring.

We have a master-slave setup in AWS RDS using mysql. We have a db.m4.xlarge for both of the instances. One of the tables is performing very slow on the read replica.

Table - user_exercises

Table Size - 3.9GB

Rows - 273499

Query - select count(*) from user_exercises;

The table has a primary key only as an index. On the master it takes < 0.1 second. On the read replica it runs forever.