I'm able to create a resource policy and specify that an instance goes into it, but is it possible to find out which availability domain an instance is in, and/or specify that an instance be created into a specific availability domain. Even better, via terraform.
Would this by done via scheduling config or otherwise via affinity/anti-affinity?
Related
If I have multiple Hazelcast cluster members using the same IMap and I want to configure the IMap in a specific manner programmatically, do I then need to have the configuration code in all the members, or should it be enough to have the configuration code just once in one of the members?
In other words, are the MapConfigs only member specific or cluster wide?
Why I'm asking is that Hazelcast documentation http://docs.hazelcast.org/docs/latest/manual/html-single/index.html#configuring-programmatically
says that
As dynamically added data structure configuration is propagated across
all cluster members, failures may occur due to conditions such as
timeout and network partition. The configuration propagation mechanism
internally retries adding the configuration whenever a membership
change is detected.
this gives me the impression that the configurations propagate.
Now if member A specifies a certain MapConfig for IMap "testMap", should member B see that config when it does
hzInstance.getConfig.findMapConfig("testMap") #or .getMapConfig("testMap")
In my testing B did not see the MapConfig done by A.
I also tried specifying at A mapConfig.TimeToLiveSeconds(60), and at B mapConfig.TimeToLiveSeconds(10).
It seemed that the items in the IMap that were owned by A were evicted in 60 seconds, while the items owned by B were evicted in 10 seconds. This supports the idea that each member needs to do the same configuration if I want consistent behaviour for the IMap.
Each member owns certain partitions of the IMap. A member's IMap configuration has effect only on its owned partitions.
So it is normal to see different TTL values of the entries of the same map in different members when they have different configurations.
As you said, all members have should have same IMap configuration to have a cluster-wide persistent behavior.
Otherwise, each member will apply its own configuration to its own partitions.
But if add a dynamic configuration as described here, then that configuration is propagated to all members and change their behavior as well.
In brief, if you add the configuration before creating the instance, that is local configuration. But, if you add it after creating the instance, that is dynamic configuration and propagates to all members.
The question is, how to update a constant? This sounds like a stupid question, but let's look at the background of my issue:
Background
I manage a network of servers, which includes a MySQL server, multiple HTTP servers, and a Minecraft server (a self-hosted server that gamers who have installed Minecraft can connect to and play together). All of the user-end services (HTTP servers, Minecraft server, user apps) are directly or indirectly related to the MySQL server. The MySQL database stores different data for each player account, for example, the online/offline status of players, etc.
In programming, constants are used to create a general reference to a value that will not change across a runtime. Especially, for software-internal identifiers, such as data flags, bitmasks, etc. In my case, I also use constants to store specific data, such as the MySQL server's address and other credentials. So when I want to change the server address, I only need to modify them from one point, for example, an internal constants.php of the server.
Problem
When I migrate my MySQL database to another host or change password, I have to update the details on every server. It is not possible to create a centralized data provider that provides the server address, because the MySQL server itself is the centralized data provider. That means, every time I change the value, I must update all servers. I must also maintain a very private and local list (probably has to be written down on a memo and stick it on my computer!) of all these places, because it is really hard to locate all these references. So, my question is, is there a better way of management that allows me to change the values from one place? Note that the servers are on different hosts, so it is not possible to put it in a local file, and it doesn't sound reasonable to create a centralized data provider (call it password provider) to provide access of the real centralized data provider (MySQL) either, since if I have the need to change the MySQL database details, I have the same need to change the password provider details as well.
This is less a concern. but since it is a similar question, I am putting it down here too. I use integer bitmasks to store player ranks. For example, if the player is a VIP, he has a 0x01 flag, and if the player is a moderator, he has a 0x10 flag, and 0x11 if both VIP and moderator, vice versa. I want to refactor the bitmask values as well, but it would be great trouble, because I need to shut down all servers and update the MySQL values, update constants on every server, then restart all servers, to avoid potential security vulnerability in the period of updating. Is there a more convenient way to do that?
This is a network management question too, but I consider it more programming-related.
We are talking about deployment system. For example we can use
capistrano: https://github.com/capistrano/capistrano. We need to
save constants.php to git and create task in capistrano for deploy
this file to each server. I use this tool for deploying of projects which are one of the 50 busiest sites of the Russian segment of the Internet:)
We are talking about data migration. So there are several ways. Some of them with downtimes and some not (sometimes it depends on the situation).
Data migration without downtime:
modify your app so it will understand old variant of players bitmask
and new one
deploy modified app
update bitmask into your databases
modify your app so it will understand only new variant of bitmasks
deploy modified app
how do I add a NIC to a compute engine instance? I need more then one NIC so I can build out an environment...I've looked all over and there is nothing on how to do it...
I know it's probably some API call through the SDK, but I have no idea, and I can't find anything on it.
EDIT:
It's the rhel6 image. figured I should clarify.
The question is probably old and a lot has changed since. Now it's definitely possible to add more nics to an instance but only at creation time (you can find a networking tab on the create instance page on the portal - corresponding rest api exists too). Each nic has to connect to a different virtual network, so you need to create more before creating the instance (if you don't have already).
Do you need an external address or an internal address? If external, you can use gcutil to add an IP address to an existing instance. If internal, you can configure a static network address on the instance, and add a route entry to send traffic for that address to that instance.
I was looking for similiar thing (to have a VM which runs Apache and nginx simultaneously on different IPs), but it seems like although you can have multiple networks (up to 5) in a project and each network can belong to multiple instances, you can not have more than one network per instance. From the documentation:
A project can contain multiple networks and each network can have multiple instances attached to it. [...] A network belongs to only one project and each instance can only belong to one network.
I've setup a cloudfront distribution pointing to my EC2 instance (web server), tucked inside a ELB.
I'm an unsure if this cloudfront domain name will ever change? (I.E when enabling/disabling it, attaching/reattaching etc.
So long as the distribution still exists, it will use the same domain on cloudfront (the one assigned to you at the distribution's creation time). This cloudfront domain will only be lost when a distribution is deleted:
A disabled distribution is no longer functional and you will no longer
be charged, but it can be enabled again at any time. A deleted
distribution is no longer accessible and is lost forever.
If you want to preserve the assigned cloudfront domain but temporarily disable access to it, use the AWS console to disable it - not delete it.
The only reason I've had to delete distributions is for general cleanup of old ones, or when I've been close to their limit of 100 distributions per account (which has only happened once to me).
For even greater control, you also have the option of mapping your own domain name to a distribution using a CNAME record:
In CloudFront, an alternate domain name, also known as a CNAME, lets
you use your own domain name (for example, www.example.com) for links
to your objects instead of using the domain name that CloudFront
assigns to your distribution.
The above is the approach I use because I like more control over resources, but depending on your use case it might be overkill since the original distribution name won't change unless you delete it.
I have a client software program used to launch alarms through a central server. At first it stored configuration data in registry entries, now in a configuration XML file. This configuration information consists of Alarm number, alarm group, hotkey combinations, and such.
This client connects to a server using a TCP socket, which it uses to communicate this configuration to the server. In the next generation of this program, I'm considering moving all configuration information to the server, which stores all of its information in a SQL database.
I envision using some form of web interface to communicate with the server and setup the clients, rather than the current method, which is to either configure the client software on the machine through a control panel, or on install to ether push out an xml file, or pass command line parameters to the MSI. I'm thinking now the only information I would want to specify on install would be the path to the server. Each workstation would be identified by computer name, and configured through the server.
Are there any problems or potential drawbacks of this approach? The main goal is to centralize configuration and make it easier to make changes later, because our software is usually managed by one or two people at most.
Other than allowing for the client to function offline (if such a possibility makes sense for your application), there doesn't appear to be any drawback of moving the configuration to a centralized location. Indeed even with a centralized location, a feature can be added in the client to cache the last known configuration, for use when the client is offline).
In case you implement a [centralized] database design, I suggest to consider storing configuration parameters in an Entity-Attribute-Value (EAV) structure as this schema is particularly well suited for parameters. In particular it allows easy addition and removal of particular parameters and also the handling parameters as a list (paving the way for a list-oriented display as well in the UI, and therefore no changes needed in the UI either when new types of parameters are introduced).
Another reason why configuartion parameter collections and EAV schemas work well together is that even with very many users and configuration points, the configuration data remains small enough that is doesn't suffer some of the limitations of EAV with "big" tables.
Only thing that comes to mind is security of the information. In either case you probably have that issue though. Probably be easier to interface with though with a database as everything would be in one spot.