You cannot move an existing EC2 instance to a different availability zone directly.

However, the following approach can be used to move an instance to a different availability zone indirectly through a new AMI:

1. Stop (do not terminate!) the old instance in the old availability zone.

2. Create an AMI based on the old instance.

3. Run a new instance of the new AMI in the new availability zone.  It will be a fairly exact copy of your old instance.

If you were using an Elastic IP address, re-associate it with the new instance.

Once you have tested the new instance and know that it&#39;s working well, terminate the old instance in the old availability zone.


How do I gzip compress a string in Python?

[`gzip.GzipFile`](https://docs.python.org/2/library/gzip.html#gzip.GzipFile) exists, but that&#39;s for file objects - what about with plain strings?


How do I gzip compress a string in Python?

In someone else&#39;s code I read the following two lines:

    x = defaultdict(lambda: 0)
    y = defaultdict(lambda: defaultdict(lambda: 0))

As the argument of defaultdict is a default factory, I think the first line means that when I call x[k] for a nonexistent key k (such as a statement like v=x[k]), the key-value pair (k,0) will be automatically added to the dictionary, as if the statement x[k]=0 is first executed. Am I correct?

And what about y? It seems that the default factory will create a defaultdict with default 0. But what does that mean concretely? I tried to play around with it in Python shell, but couldn&#39;t figure out what it is exactly.


Python defaultdict and lambda

Sometimes when trying to launch my t1.micro EC2 instance, it cannot be provisioned and Amazon recommends trying a different availability zone. Is it possible to change this for an existing instance?

Is it possible to change the availability zone of an existing EC2 t1.micro instance?

<p>Sometimes when trying to launch my t1.micro EC2 instance, it cannot be provisioned and Amazon recommends trying a different availability zone. Is it possible to change this for an existing instance?</p>


I tried mongo replica sets for the first time.

I am using ubuntu on ec2 and I booted up three instances.
I used the private IP address of each of the instances.  I picked on as the primary and below is the code.

    mongo --host Private IP Address
    rs.initiate()
    rs.add(“Private IP Address”)
    rs.addArb(“Private IP Address”)

All at this point is fine.  When I go to the http://ec2-xxx-xxx-xxx-xxx.compute-1.amazonaws.com:28017/_replSet site I see that I have a primary, seconday, and arbitor.

Ok, now for a test.  

On the primary create a database in this is the code:

    use tt
    db.tt.save( { a : 123 } )

on the secondary, I then do this and get the below error:

    db.tt.find()
    error: { &quot;$err&quot; : &quot;not master and slaveOk=false&quot;, &quot;code&quot; : 13435 }

I am very new to mongodb and replicates but I thought that if I do something in one, it goes to the other.  So, if I add a record in one, what do I have to do to replicate across machines?

mongodb, replicates and error: { &quot;$err&quot; : &quot;not master and slaveOk=false&quot;, &quot;code&quot; : 13435 }

We&#39;re using Amazon EC2, and we want to put an ELB (load balancer) to 2 instances on a private subnet. If we just add the private subnet to the ELB, it will not get any connections, if we attach both subnets to the ELB then it can access the instances, but it often will get time-outs. Has anyone successfully implemented an ELB within the private subnet of their VPC? If so, could you perhaps explain the procedure to me?

Thanks

Amazon ELB in VPC

What `scp` arguments should I use to download a file from an Amazon EC2 instance to local storage?

How Can I Download a File from EC2

I have a server running the recent Ubuntu AMIs from Canonical. The size of the EBS boot volume is 8GB. I know that I can resize EBS volumes by taking a snapshot, creating a new volume and expanding the partition on it. How can I increase the size of the volume while the machine is running? If this is not possible, what is the preferred method for increasing the boot volume size with minimal downtime?

How do I increase the EBS volume size of a running instance?

We are starting instances, and accessing the user-data we place. But does anybody understand the internals of this operation (from Amazon&#39;s side)? When we pass in the user-data, at what point is that data transmitted to the VM (is this a Xen feature) and where is it stored?

I first thought, it was set as the USER_DATA env var, but we can also pass it as a file. Where is that file stored? Is it generic to all instances or varies depending on AMI?

This is not a problem per se, just wanted to know how Amazon does this.

User data screenshot: http://d.pr/GZlY

Amazon ec2 user-data, how does it work?

I have a java project that runs on a webserver. I always hit this exception.

I read some documentation and found that pessimistic locking (or optimistic, but I read that pessimistic is better) is the best way to prevent this exception.

But I couldn&#39;t find any clear example that explains how to use it.

My method is like:

```
    @Transactional
    public void test(Email email, String subject) {
        getEmailById(String id);
        email.setSubject(subject);
        updateEmail(email);
    }
```

while:

 * `Email` is a Hibernate class (it will be a table in the database)
 * `getEmailById(String id)` is a function that returns an `email` (this method is not annotated with `@Transactional`)
 * `updateEmail(email)`: is a method that updates the email.

*Note:* I use Hibernate for save, update &amp; so on (example: `session.getcurrentSession.save(email)`)

*The exception:*

    ERROR 2011-12-21 15:29:24,910 Could not synchronize database state with session [myScheduler-1]
    org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [email#21]
        at org.hibernate.persister.entity.AbstractEntityPersister.check(AbstractEntityPersister.java:1792)
        at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:2435)
        at org.hibernate.persister.entity.AbstractEntityPersister.updateOrInsert(AbstractEntityPersister.java:2335)
        at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:2635)
        at org.hibernate.action.EntityUpdateAction.execute(EntityUpdateAction.java:115)
        at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:279)
        at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:263)
        at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:168)
        at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)
        at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50)
        at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1027)
        at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:365)
        at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:137)
        at org.springframework.orm.hibernate3.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:656)
        at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:754)
        at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:723)
        at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:393)
        at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:120)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
        at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
        at $Proxy130.generateEmail(Unknown Source)
        at com.admtel.appserver.tasks.EmailSender.run(EmailNotificationSender.java:33)
        at com.admtel.appserver.tasks.EmailSender$$FastClassByCGLIB$$ea0d4fc2.invoke(&lt;generated&gt;)
        at net.sf.cglib.proxy.MethodProxy.invoke(MethodProxy.java:149)
        at org.springframework.aop.framework.Cglib2AopProxy$CglibMethodInvocation.invokeJoinpoint(Cglib2AopProxy.java:688)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
        at org.springframework.aop.aspectj.AspectJAfterThrowingAdvice.invoke(AspectJAfterThrowingAdvice.java:55)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:161)
        at org.springframework.aop.framework.adapter.AfterReturningAdviceInterceptor.invoke(AfterReturningAdviceInterceptor.java:50)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:161)
        at org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor.invoke(MethodBeforeAdviceInterceptor.java:50)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:161)
        at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:89)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
        at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:621)
        at com.admtel.appserver.tasks.EmailNotificationSender$$EnhancerByCGLIB$$33eb7303.run(&lt;generated&gt;)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.springframework.util.MethodInvoker.invoke(MethodInvoker.java:273)
        at org.springframework.scheduling.support.MethodInvokingRunnable.run(MethodInvokingRunnable.java:65)
        at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:51)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
        at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:317)
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:150)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$101(ScheduledThreadPoolExecutor.java:98)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.runPeriodic(ScheduledThreadPoolExecutor.java:180)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:204)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:680)
    ERROR 2011-12-21 15:29:24,915 [ exception thrown &lt; EmailNotificationSender.run() &gt; exception message Object of class [Email] with identifier [211]: optimistic locking failed; nested exception is org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [Email#21] with params ] [myScheduler-1]
    org.springframework.orm.hibernate3.HibernateOptimisticLockingFailureException: Object of class [Email] with identifier [21]: optimistic locking failed; nested exception is 

Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect)

I noticed that there does not seem to be an option to download an entire `s3` bucket from the AWS Management Console.

Is there an easy way to grab everything in one of my buckets? I was thinking about making the root folder public, using `wget` to grab it all, and then making it private again but I don&#39;t know if there&#39;s an easier way.

Downloading an entire S3 bucket?

I have some basic understanding what [Amazon SimpleDB][1] is, but according to the [Amazon DynamoDB][2] description it seems to be almost the same: a [NoSQL Key-value store][3] service.

Can someone simply explain the **main differences** between them and tell in which cases to choose **one over the other**.


  [1]: http://aws.amazon.com/simpledb/
  [2]: http://aws.amazon.com/dynamodb/
  [3]: http://en.wikipedia.org/wiki/NoSQL#Key-value_store

Amazon SimpleDB vs Amazon DynamoDB

I have AWS account. I&#39;m using S3 to store backups from different servers. The question is there any information in the AWS console about how much disk space is in use in my S3 cloud?

AWS S3: how do I see how much disk space is using

Is anyone aware of an Amazon API that allows you to purchase items programmatically?

I looked at tons of their web services (Product Advertising, MWS, etc.), and none of them seemed to do this.

I found this thread that seemed to suggest there was no solution, but there was no definitive answer: https://forums.aws.amazon.com/thread.jspa?threadID=45127

Just to be clear, I want to make a purchase with MY payment details, not on behalf of any user. I figured if ANYONE supported this, it would be Amazon. But I realize there may be business (security?) reasons not to support this as well...

Content Type	Original Author	Original Content on Stackoverflow
Question	anon	View Question on Stackoverflow
Solution 1 - Amazon Ec2	Eric Hammond	View Answer on Stackoverflow

Is it possible to change the availability zone of an existing EC2 t1.micro instance?

Amazon Ec2 Problem Overview

Amazon Ec2 Solutions

Solution 1 - Amazon Ec2

Python defaultdict and lambda

How do I gzip compress a string in Python?

Attributions