New Amazon CloudWatch Action – Reboot EC2 Instance

Amazon CloudWatch monitors your cloud resources and applications, including Amazon Elastic Compute Cloud (EC2) instances. You can track cloud, system, and application metrics, see them in graphical form, and arrange to be notified (via a CloudWatch alarm) if they cross a threshold value that you specify. You can also stop, terminate, or recover an EC2 instance when an alarm is triggered (see my blog post, Amazon CloudWatch – Alarm Actions for more information on alarm actions).

New Action – Reboot Instance
Today we are giving you a fourth action. You can now arrange to reboot an EC2 instance when a CloudWatch alarm is triggered. Because you can track and alarm on cloud, system, and application metrics, this new action gives you a lot of flexibility.

You could reboot an instance if an instance status check fails repeatedly. Perhaps the instance has run out of memory due to a runaway application or service that is leaking memory. Rebooting the instance is a quick and easy way to remedy this situation; you can easily set this up using the new alarm action. In contrast to the existing recovery action which is specific to a handful of EBS-backed instance types and is applicable only when the instance state is considered impaired, this action is available on all instance types and is effective regardless of the instance state.

If you are using the CloudWatch API or the AWS Command Line Interface (CLI) to track application metrics, you can reboot an instance if the application repeatedly fails to respond as expected. Perhaps a process has gotten stuck or an application server has lost its way. In many cases, hitting the (virtual) reset switch is a clean and simple way to get things back on track.

Creating an Alarm
Let’s walk through the process of creating an alarm that will reboot one of my instances if the CPU Utilization remains above 90% for an extended period of time. I simply locate the instance in the AWS Management Console, focus my attention on the Alarm Status column, and click on the icon:

Then I click on Take the action, choose Reboot this instance, and set the parameters (90% or more CPU Utilization for 15 minutes in this example):

If necessary, the console will ask me to confirm the creation of an IAM role as part of this step (this is a new feature):

The role will have permission to call the “Describe” functions in the CloudWatch and EC2 APIs. It also has permission to reboot, stop, and terminate instances

I click on Create Alarm and I am all set!

This feature is available now and you can start using it today in all public AWS regions.


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Raspberry PI 2 Cluster Case Pt2

From Raspberry PI 2 Cluster Case pt1, I drew up a rough sketch with certain goals I set out to. They are,

  1. Able to fit in 6 RPI2 in a small, contained volume.
  2. Has to be stackable.
  3. Able to fit in a power supply and a 8 port network switch for the 6 RPI2.
  4. Able to cool off the cluster with no fan.
  5. Has to be cheap.


I then cut out an Acrylic panel at a near laser shop.

Two RPI2 on a cluster panel

The panel have two big round holes for ventilation, 8 holes for RPI2 mounts, and 8 more holes for pillar screws.

Once you put pillars, it looked like this.

Pillar Screws and mounts on a cluster panel

I put a giant square hole in the center to put a USB charger as power supply. You can see the two big round holes for heat ventilation.

At this point, I was terrorized with fact that I could not put a USB-to-MicroUSB cable to the center USB charger. You see the square hole is completely closed? I found that the panel blocked the USB charger’s USB socket, rendering the charger useless. What a bummer…

Gah! No way!

Of course, my happy story did not end there. I then put a RPI to see if it fitted in. To my disappointment, the mount was just too high. You see USB ports sticks to the upper level panel, and there is space underneath the RPI? That’s bad.

Long Mount
High Mountain

In fact, the mount was just too Long. I figured a mount should be around 4~5 mm in length. On top of that, I put one too many pillar screws. I had to use only the minimum number of them to maintain structure strength.

All in all, three problems.

  1. Entrance to USB charger.
  2. Appropriate Mount screw.
  3. Minimum # of pillar screws.

The Final Result

After Fixing three issues above, I now have this.

6 Nodes RPI2 Cluster
6 Nodes RPI2 Cluster
The cluster from different angle.

Those USB-to-MicroUSB cables are only 30 centimeters in length. They still stand out and take up quite a bit of space. Does anyone know where I can get a shorter cable?

8 Ports Network Switch at the bottom stack
8 Ports Network Switch at the bottom stack

Of course You can put the entire cluster on your desk.

A cluster on a desk
A cluster on a desk


I’ve run the cluster closed to two months so far. I’ve experienced neither heat issue nor performance hit. No single node has gone down while I’m running Apache Spark/Hadoop in cluster mode. It has been amazingly stable and easy to operate. Although there are few more issues I like to fix up later. (Especially the USB charger cable.)

Let’s move on to JAVA on Raspberry PI next time.

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City Creator

Choose a city from the selection on the right, and click the corresponding ‘build’ button to begin.

Drag and drop pieces from the palettes on the left onto the space on the right. Clicking on a piece brings it to the front.

Arrange them to make your city. (It might help to start by adding the roads)

You can delete your whole town by clicking the ‘Delete all’ button.

Click ‘Save & send’ to send your unique city to your friends.

Have fun,
The Construction Crew

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Why Britain has ‘ghost trains’

BBC Britain

The train that cuts across the West Yorkshire countryside from Leeds to the small town of Snaith departs just once at precisely 17:16, Monday to Saturday. Return trains depart twice: one at 07:16, one at 19:01.

Given these infrequent departures, you’d expect packed carriages. But on a recent Friday rush hour – when Leeds train station, the second-busiest in the UK outside London, is swirling with commuters – no one, aside from me and my companions, remains on the line for more than a few stops. Soon, one carriage after another becomes completely, eerily empty. You could cartwheel down the aisles.

The Leeds-Snaith line is what rail enthusiasts call a ghost train; Snaith station, a ghost station. The webpage about Snaith on ticket sales site warns that ticket machines are not available at the station. Nor is there a ticket office, taxi rank or cab office.

It’s one of many train services around Britain that run with empty carriages – sometimes once or twice a day, sometimes as rarely as once a week. Sometimes even ticket sellers don’t know they exist, and it takes dedicated amateurs to seek them out. So why do these trains run at all?

The whisper of a service

There is no single definition of what constitutes a ghost train, although the general consensus is that it’s when a service is so infrequent, the train becomes effectively useless. Slippery or not, though, the term “ghost train” seems apt. It implies a service that is not exactly whole – something that whispers through towns and countryside, leaving barely a dent in its wake.

Only a special few even know that ghost trains exist

Perhaps most important of all, the term ghost train implies something that only a special few know exists. The press contact of the National Rail Museum of York, for example, was baffled by my request for an interview about ghost trains, thinking I wanted to discuss “haunted items” in the museum’s collection. 

Nobody knows exactly how many ghost trains there are. On the website The Ghost Station Hunters, run by rail enthusiasts Tim Hall-Smith and Liz Moralee, there are 37 listed, and those are only the stations the intrepid pair has gotten to and written about so far. Hall-Smith says he’s counted more than 50 by looking through timetables.

Official figures are difficult to track down. Northern Rail, which runs the Leeds to Snaith line, said they have six parliamentary train services; that’s out of 2,500 services they run each day. But a request from the Department of Transport for overall numbers turned up nil: “The department doesn’t hold a definitive list of these low-frequency routes, because we don’t use the terminology of ghost train – there’s no formally agreed definition of what would constitute one,” says Andrew Scott, one of the Department of Transport’s press officers.

Chasing trains

The sheer mystery of ghost trains is part of what makes them compelling to a small, but passionate, community of “ghost train hunters” that, Hall-Smith and Moralee say, spans the globe, sharing information online through websites like theirs. Hall-Smith has been chasing the trains since 1993, visiting 41 ghost stations. Moralee has visited 32. They take pictures at each one and try to put them on their website, with detailed descriptions about how to get there and what to expect. To celebrate his 50th birthday, they went to Berney Arms in Norfolk. “It has to be one of the maddest places we have both been to,” he says. “No words can describe how isolated this place was.” The closest road was three miles away; the only nearby structures were a shuttered pub and an old windmill.

It’s a passion that takes commitment. Since the trains are run on extremely inconvenient schedules, sometimes without a return trip, sometimes before sunrise, the journey means a lot of legwork. If there is anyone else on the train, it’s probably another ghost train enthusiast.

It’s a useless, limited service. But there would be a stink if anyone tried to close it

Given the overcrowding on Britain’s trains, it may seem odd for these empty carriages to ride the rails – or for empty stations to stand sentry over them. From 1995-96 to 2011-12, the total number of miles ridden by train passengers leapt by 91%, while the entire UK train fleet grew by only 12%.

“Ghost trains are there just for a legal placeholder to prevent the line from being closed,” says Bruce Williamson, national spokesperson for the advocacy group RailFuture. Or as Colin Divall, professor of railway studies at the University of York, puts it: “It’s a useless, limited service that’s borderline, and the reason that it’s been kept is there would be a stink if anyone tried to close it.”

Why ghosts exist

That is the crux of why the ghost trains still exist. A more official term is “parliamentary trains”, a name that stems from past years when an Act of Parliament was needed to shut down a line. Many train operators kept running empty trains to avoid the costs and political fallout – and while this law has since changed, the same pressures remain.

Closing down a line is cumbersome. There must first be a transport appraisal analysing the effect of a closure on passengers, the environment and the economy. The proposal is submitted to the Department of Transport and at that point its details must be published in the press, six months ahead of the closure. Then comes a 12-week consultation period, during which time anyone is welcome to protest; public hearings are sometimes held, especially if the closure is controversial. Then, finally, the plans are submitted to the Office of Rail and Road, who decide if the line closes.

As a result it often costs less – in terms of time, paperwork and taxpayers’ money – to keep a line running at a bare minimum. Other nations run limited service trains, but experts say that the particular politicisation of Britain’s railways – and the creation of so many steps required to close them – means that when people say “ghost trains,” they’re usually referring to British ones.

There’s a more optimistic reason for running a ghost train, too: it shows hope that the line may be used more regularly again in the future. Once a service is closed entirely, infrastructure deteriorates; even if the physical track is kept, it becomes overgrown. Not to mention that drivers then would have to be re-trained on the track, or that a whole new slew of paperwork would have to be gone through to re-open it. Starting from scratch, in other words, is far more expensive than maintaining what you have.

Some ghost services have come back from the dead

The Halton Curve is one example. A half-mile connection between two lines that are frequently serviced, it operated for years as a ghost train. After years of advocates defending its potential, if run more regularly, to provide service from North Wales into Liverpool, plans were finally announced last year to give it a £10.4 million upgrade and re-establish the link, returning it to full service.

Experts say that Halton Curve is emblematic of an ongoing trend. Closing lines is particularly rare these days. It’s far more common to see new lines opening or limited service lines being returned to full service. Ghost trains, in other words, may be at risk.

That’s good news for railway advocates who want to see the country better connected by more efficient, frequently running trains. But it may be bad news to those like Hall-Smith and Moralee, who have built a lifelong passion out of tracking the ghosts down.

There is no train to Snaith

On our ride to Snaith, the two tell me about the trouble Moralee had procuring her ticket. The Snaith train was listed on the board of departures, but the person at the ticket desk still hadn’t heard of it. “You must be mistaken,” he’d told her. “There is no train to Snaith.”

“That’s what we love about this,” Hall-Smith says: knowing a secret that, in the hyper-organised and planned world of rail transport, shouldn’t exist. A secret that not even everyone who works in that world knows exists.

A ghost train might be a bureaucratic hangover. It might be a fiscal headache. It might be a waste of resources and potential. But in the world of transport and infrastructure, where efficiency and budgets rule, it’s also a quirky aberration – one that might not be around forever, but that, for now, provides an acute sense of joy to a small, passionate group of people who love it for its Alice-in-Wonderland-style absurdity.

This story is a part of BBC Britain – a new series focused on exploring this extraordinary island, one story at a time. Readers outside of the UK can see every BBC Britain story by heading to the Britain homepage; you also can see our latest stories by following us on Facebook and Twitter.

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LearnLeo May Help you Streamline Studying

LearnLeo an online platform that allows law students to categorize case information, and organize briefs and outlines with the click of a button. The company estimates it saves law students on average ten hours of work per week. S Students using LearnLeo highlight passages and choose a color that corresponds with the elements of the […]

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