DevOps Interview Questions and Answers
Question - 31 : - Explain whether it is possible to share a single instance of a Memcache between multiple projects?
Answer - 31 : -
Yes, it is possible to share a single instance of Memcache between multiple projects. Memcache is a memory store space, and you can run memcache on one or more servers. You can also configure your client to speak to a particular set of instances. So, you can run two different Memcache processes on the same host and yet they are completely independent. Unless, if you have partitioned your data, then it becomes necessary to know from which instance to get the data from or to put into.
Question - 32 : - You are having multiple Memcache servers, in which one of the memcache servers fails, and it has your data, will it ever try to get key data from that one failed server?
Answer - 32 : -
The data in the failed server won’t get removed, but there is a provision for auto-failure, which you can configure for multiple nodes. Fail-over can be triggered during any socket or Memcached server level errors and not during standard client errors like adding an existing key, etc.
Question - 33 : - Explain how you can minimize the Memcached server outages?
Answer - 33 : -
- When one instance fails, several of them go down, and this will put a larger load on the database server when lost data is reloaded as a client make a request. To avoid this, if your code has been written to minimize cache stampedes then it will leave a minimal impact
- Another way is to bring up an instance of Memcached on a new machine using the lost machines IP address
- The code is another option to minimize server outages as it gives you the liberty to change the Memcached server list with minimal work
- Setting timeout value is another option that some Memcached clients implement for Memcached server outage. When your Memcached server goes down, the client will keep trying to send a request till the time-out limit is reached
Question - 34 : - Explain how you can update Memcached when data changes?
Answer - 34 : -
When data changes you can update Memcached by
- Clearing the Cache proactively: Clearing the cache when an insert or update is made
- Resetting the Cache:It is similar to the first method but rather than just deleting the keys and waiting for the next request for the data to refresh the cache, reset the values after the insert or update.
Question - 35 : - Explain what Dogpile effect is? How can you prevent this effect?
Answer - 35 : -
Dogpile effect is referred to the event when a cache expires, and websites are hit by the multiple requests made by the client at the same time. This effect can be prevented by using a semaphore lock. In this system when value expires, the first process acquires the lock and starts generating new value.
Question - 36 : - Explain how Memcached should not be used?
Answer - 36 : -
- Memcached common misuse is to use it as a data store, and not as a cache
- Never use Memcached as the only source of the information you need to run your application. Data should always be available through another source as well
- Memcached is just a key or value store and cannot perform a query over the data or iterate over the contents to extract information
- Memcached does not offer any form of security either in encryption or authentication
Question - 37 : - When a server gets shut down does data stored in Memcached is still available?
Answer - 37 : -
Data stored in Memcached is not durable, so if a server is shut down or restarted, then all the data stored in Memcached is deleted.
Question - 38 : - Mention what the difference between Memcache and Memcached?
Answer - 38 : -
Memcache: It is an extension that allows you to work through handy object-oriented (OOP’s) and procedural interfaces. It is designed to reduce database load in dynamic web applications.
Memcached: It is an extension that uses the libmemcached library to provide API for communicating with Memcached servers. It is used to increase the dynamic web applications by alleviating database load. It is the latest API.
Question - 39 : - Explain Blue/Green Deployment Pattern
Answer - 39 : -
Blue/Green coloring pattern addresses the most important challenges faced during the automatic deployment process. In Blue/ Green Deployment approach, you need to ensure two identical production environment. However, only one among them is LIVE at any given point of time. The LIVE environment is called Blue environment.
When the team prepares the next release of their software, they conduct their final stage of testing in an environment which is known as Green environment. Once verified, the traffic is routed to the Green environment.
Question - 40 : - What are the containers?
Answer - 40 : -
Containers are from of lightweight virtualization. They offer isolation among processes.