Today we continue to compare networking capabilities in the azure and aws public clouds. We compared Security, Security Groups, Network ACLs, Custom routing tables, Virtual network interfaces, DNS service, connectivity, VPN over IPSec, private connectivity over Exchange, SDK & Tools.We also reviewed CDN And traffic Manager from Azure. Let us look at VPN Gateway.
A VPN Gateway is a type of virtual network gateway that sends encrypted traffic across a public connection.  A VPN gateway can be of two types - ExpressRoute and vpn.  We are interested only in the latter category. A multisite connection establishes multiple connections to the same vpn gateway.
In such a setting, all the VPN tunnels share the available bandwidth for the gateway. Using the powershell and Azure portal, a vpn gateway settings can be configured.

#puzzle
There are three boxes of gold, silver and mixture. These boxes are all labeled incorrectly. How can we tell them apart if we are given only one choose to pick and open a box.
Solution. The box that is labeled mixed should be chosen. If it turns out to be silver, the box labeled silver will gold and the other will be mixed. If it is gold, the other two can similarly be found.  The mixture may contain silver or gold on the top layer, the label can still tell apart the similar looking content.

#codingexercise
Given k as number of floors and n as number of eggs, find the minimum number of trials needed to determine which floor is the highest and yet safe to drop an egg from.

int GetTrials(int n, int k)
{
if (k == 1 || k == 0) return k;

if ( n == 1) return k;
int min = INT_MAX;
for ( int i = 1; i <= k; i++)
{
    int result =  Math.max(GetTrials(n-1, k-1), GetTrials(n, k-i));
    if (result < min)
         min = res;
}
return min + 1;
}
Another way to look at it is to divide the floors by 2 for each egg drop. each subsequent egg in its lifetime divides and narrows down  the range further
// pseudocode to illustrate
assert(log(floors) <= eggs);
void GetTrials(int floors, int eggs, int int start, int end,  ref int trial)
{
if (start==end || eggs == 0) return;
int next = start+1;
for (int i = 0; 2^i <= end; i++)
     if (2^i > start) {
          next = 2^i;
          break;
     }
next = min(next, (start+end)/2);      
if (break(next))
{
end = next;
trials +=1;
eggs --;
GetTrials( floors, eggs, start, end, ref trials);
}else{
start = next;
trials += 1:
GetTrials(floors, eggs, start, end, ref trials);
}
}

Today we continue to compare networking capabilities in the azure and aws public clouds. We compared Security, Security Groups, Network ACLs, Custom routing tables, Virtual network interfaces, DNS service, connectivity, VPN over IPSec, private connectivity over Exchange, SDK & Tools. Now we review CDN And traffic Manager from Azure.
CDN delivers content to end users through a robust network of global data centers. It cuts the time that it takes to serve up content to the web applications by caching closer to the user than the origin. Using the CDN, we can cache publically available objects loaded from Azure blob storage, web application, virtual machine, application folder and other HTTP/HTTPS location.  The content is typically static such as images, stylesheets, documents, files, client-scripts and HTML pages and dynamic content such as PDF report and graph can also be served. CDN does not do this for each request and can even serve up entire websites from its cache. Generally video benefits immensely from the low latency.The locations are regional and chosen to maximize the bandwidth to the clients. It should be noted that the clients can be mobile and a host of data could come from the Internet of Things (IoT) but as data grows the CDNs cache more locally to the clients thus enabling better user experience.
Traffic manager routes incoming traffic for high performance and availability. Traffic manager distributes the user traffic for service endpoints in different datacenters. These endpoints can be Azure VMs, endpoints and cloud services. However, Traffic Manager can also be used with external non-Azure endpoints. Traffic Manager uses the Domain Name System to direct client requests to the most appropriate endpoint based on a traffic routing method and the health of the endpoints. Traffic Manager provides a range of traffic routing methods to suit different application needs, endpoint health monitoring and automatic failover.  Thus it can improve availability, responsiveness, allow maintenance without downtime, combine on-premise and cloud based applications and distribute traffic for large, complex deployments.


#codingexercise
We look at the tree construction method for finding the different interpretations for a sequence of digits.

Node GetTree(List<int>A, String b, int prev)
{
if (prev > 26)
     return null;
var newb = b + prev.ToLetter();
var root = new Node(){b};
if (A.Count != 0)
{
     prev = A[0];
     root.left = GetTree(prev, newb, A.GetRange(1, A.Count - 1));
     if (A.Count > 1) {
       prev = A[0]*10 + A[1];
       root.right = GetTree(prev, newb, A.GetRange(2, A.Count-2));
     }
}
return root;
}

Then we can print the leaves of this tree as ABA, AU, LA for {1,2,1}

Given a value N, if we want to make change for N cents, and we have infinite supply of each of S = { S1, S2, .. , Sm} valued coins, how many ways can we make the change? The order of coins doesn’t matter.
int GetCount(List<int> coins, int num, int sum)
{
if (sum == 0) return 1;
if (sum < 0) return 0;
if (num <= 0 && sum >= 1) return 0;
return GetCount(coins, num-1, sum) + GetCount(coins, num, sum-coins[num-1]);
}
we could also do the same with combinations where we take one or more of the same coins as long as the sum is not exceeded.

Today we continue to compare networking capabilities in the azure and aws public clouds. We compared Security, Security Groups, Network ACLs, Custom routing tables, Virtual network interfaces. We now compare DNS service, connectivity, VPN over IPSec, private connectivity over Exchange, SDK & Tools,  AWS provides Route53 as a highly available and scalable DNS web service. We can register domain names, route internet traffic to the resources for the domain and check the health of the resources. The domain registry is with Verisign.  When we register a domain name, Amazon route 53 automatically creates a public hosted zone that has the same name as the domain and to route traffic to our resources, we create resource record sets. When an end user requests a name, the request is routed to a name resolver which forwards it to the DNS root name server. With the response the name resolver forwards it to the TLD name server for the .com domains. Again with the response, the name resolver forwards it to the route 53 name server which then provides the ip address for the name. The resolver then returns this to the user.
Azure uses Anycast networking  so that each DNS query is answered by the closest available DNS server thus increasing the performance and the availability of the domain.
VPN gateway provides connectivity between the virtual network in the cloud and the on-premise site. The Azure VPN gateway is a virtual network gateway that sends encyrpted traffic over a public connection. Azure provides two types of gateways - ExpressRoute and VPN. There can be only one gateway of each type in a virtual private network. A VPN gateway allows point to site as well as multisite that share bandwidth available to the gateway. AWS provides Direct Connect links that lets you create virtual interfaces directly to the AWS cloud and Amazon Virtual Private cloud, bypassing the ISPs in the route. Both cloud providers allow public ip addresses to be assigned to virtual machine instances there by providing internet connectivity. In order to service, large customers with heavy bandwidth requirements, both cloud providers seem to have agreements with major Telecom providers and ISVs to offer private connectivity between their clouds and the customer's premise. While AWS doesn't provide SLA for this service, Azure provides 99.9 % SLA.  Azure and AWS provide programmable SDKs as well as CLI and REST APIs. These significantly improve automation and workflow expansion.
#codingexercise
Find all possible interpretation of an array of digits.
For example 121 can be aba au la
We can decode a tree and print the leaves from the root for the interpretations. This is similar to dynamic programming as shown below:

void decode(List<int> A, int? prev, ref StringBuilder b)
{
if (A.empty()) { b+= ToLetter(prev); // null has no effect
                          Console.WriteLine(b.toString());
                          b -= ToLetter(prev);
                          return;}
if (prev !=  null) {
char c =  ToLetter(prev*10+A[0]); // data more than 26 has no effect
if (c.isValid()){
b+= c;
Decode( A.GetRange(1, A.Count-1), null, ref b);
b-=c;
}
}
char c =ToLetter(A[0]);
b+= c;
Decode(A.GetRange(1,A.Count -1), null, ref b);
b-=c;
Decode (A.GetRange(1,A.Count-1), A[0], ref b);
}

Yesterday we started comparing virtual private network capabilities in public clouds. Azure started offering virtual networks from 2013 while AWS has been an early starter.  Azure's Virtual Network VN resembles AWS VPC in many aspects but we will also enumerate differences. That said Azure has kicked it up a notch.

We compared subnets which is a critical component for dividing networks. Both AWS and Azure allows any size network to be created as either single public subnet or a mix of public and private subnets. The difference is in the use of wizards which makes it super easy.
As with all networks, security is important to the network which can be configured at the instance, subnet and the overall network level.  Moreover, we can selectively permit or deny traffic using network ACLs
The use of network ACLs is complimentary to the use of security groups which helps cotnrol access Traffic can also be managed at any level using custom routing tables. By default, the routing table of the network is used unless a custom is specified. 
Additional  ip addresses can be assigned to the same instance in a network. However in order to do this, the instance has to be large enough and support multiple NIC cards. Both providers allow multiple NIC cards upto 8 only on specific large instances. 

#codingexercise
Given an integer array of n integers, find sum of bit differences in all pairs that can be formed from array elements. We gave an alternate way that involved enumerating all combinations of pairs from the array using the Combine method discussed earlier
int GetSumBitDifferencesUsingCombinations(List<int> A)
{
int ret = 0;
var pairs = new List<Tuple<int,int>>();
var seq = new List<int>();
int start = 0;
int level = 0;
Combine(pairs, ref seq, ref pairs, start, level);
pairs.ForEach ( x => ret += GetDiff(x.first, x.second));
return ret;
}
Void Combine (List<int> a, ref List<int> b, ref List<Tuple<int, int>> pairs, int start, int level)
{
For (int I = start ; I < a.Length; i++)
{
if (b.contains(a[i]) == false){
b[level] = a[i];
if (b.length == 2) {
var t = new Tuple<int, int>(){b[0], b[1]};
pairs.Add(t);
}
If (I < a.Length-1)
Combine(a,b,start+1,level+1)
B[level] = 0;
}
}
int GetDiff(uint a, uint b)
{
int ret = 0;
for (int i = 0; i < 32; i++)
{
uint c = 1 << i;
if (a & c != b & c)
         ret++;
}

return ret;
}

In the previous posts, we talked about public cloud offerings. This leads us to compare public clouds. Let us do so today with comparision of private network offerings.

Azure started offering virtual networks from 2013 while AWS has been an early starter.  Azure's Virtual Network VN resembles AWS VPC in many aspects but we will also enumerate differences. That said Azure has kicked it up a notch.

Subnets:
Subnets divide the network into smaller network and are very helpful to create private networks. AWS allows VPC to be created with
1) single public subnet
2) public and private subnets
3) public and private subnets with hardware VPN access
4) private subnet only with a hardware VPN access.
Azure also gives similar flexibility to create subnets of any size. The difference is in the use of wizards between AWS and Azure.  AWS wizards have been used for a while longer.

Security:
Security is one of the most important considerations for the virtual private network. AWS provides security services to tackle at instance level, subnet level and overall network.  Azure has simpler design. Inbound and outbound rules can be configured in both.

Security Groups:
AWS security groups helps control access and this is available from both. Azure calls it Network Security Group and it is available only for regional virtual networks. 

Network ACLs:
Azure and AWS both support network ACLs which allow users to selectively permit or deny traffic to your networks.

Custom routing tables.
subnets inherit the main routing table. In AWS, we can customize these within a subnet.In Azure, the support was somewhat limited until recently.

Virtual network interfaces
multiple NICs are allowed to be activated on virtual machine instances however both cloud providers only allow this on large instances.
documentation on Azure: https://docs.microsoft.com/en-us/azure/
documentation on AWS: https://aws.amazon.com/documentation/ 

#codingexercise

int GetMinSumSquares(List<int>positives, uint scalar)

{

if (positives == null || positives.Count == 0) return 0;
int inclusive = positives[0];
int exclusive = 0;
for (int i = 1; i < positives.Count; i++)
{
var min = Math.min(inclusive, exclusive);
inclusive  = exclusive + positives[i] × positives[i];
exclusive = min;
}
return Math.min(inclusive, exclusive);

}

Given an integer array of n integers, find sum of bit differences in all pairs that can be formed from array elements
For example bit difference for 2 represented by 010 and 7 represented by 111 is 2. Therefore an array with {2,7} will have (2,2), (2,7), (7,2) and (7,7) with sum of bit differences = 0 + 2 + 2 + 0 = 4.
int GetSumBitDifferences(List<int> A)
{
int ret = 0;
for (int i = 0; i < 32; i++)
{
int count = 0;
for (int j = 0; j < A.Count; j++)
     if (A[j] & (1 << i))
         count++;

ret += (count x (A.Count-count) x 2);
}
return ret;
}
Another way to do this would be to enumerate all combinations of pairs from the array using the Combine method discussed earlier
int GetSumBitDifferencesUsingCombinations(List<int> A)
{
int ret = 0;
var pairs = new List<Tuple<int,int>>();
var seq = new List<int>();
int start = 0;
int level = 0;
Combine(pairs, ref seq, ref pairs, start, level);
pairs.ForEach ( x => ret += GetDiff(x.first, x.second));
return ret;
}
The combinations above also include those where the first and second element are the same however there is no contribution to the result

An introduction to private cloud versus public cloud masquerading as private cloud can be found here: https://1drv.ms/w/s!Ashlm-Nw-wnWrF0qVoeSgL7Xnu1w 

Here are a few specific ways to differentiate and make the private cloud more appealing while not stealing any light from public cloud. These include

1)     Provide container resources in addition to virtual machines to explode the number of computing resource

2)     Provide services that are customized to frequent usages by private cloud customers. This includes not only making it easier to use some services but also provisioning those that many customers often use.

3)     Anticipate customer requests and suggest compute resources based on past history and measurements.

4)     Provide additional services that more customers are drawn to the services and not just to the cloud. Additionally, the customers won’t mind when the weight of the services is shifted between public and private cloud infrastructure as the costs dictate.

5)     Provide additional services that won’t be offered elsewhere. For example, data tiering, aging, archival, deduplication, file services, backup and restore, naming and labeling, accelerated networks etc. offer major differentiation that do not necessarily have to lean towards machine learning to make the private cloud smart.

6)     Offer major periodic maintenance and activities on behalf of the customer such as monitoring disk space and adding storage, checking for usages and making in place suggestions on the portal.

7)     Reduce the volume of service desk tickets aggressively with preemptive actions and minimizing them to only failures.  This is paying off debt so it may not translate to new services.

8)     Improving regional experiences not only with savvy resources but also improved networks for major regions

9)     Provide transparency, accounting and auditing so that users can always choose to get more information for self-help and troubleshooting. FAQs and documentations could be improved preferably with search field.

10)  Enable subscriptions to any or all alerts that can be setup by the customer on various activities. This gives the user informational emails with subjects that can be used to filter and treat at appropriate levels.

 #codingexercise

int GetMinSumWeightedNegatives(List<int>negatives, uint scalar)

{

if (negatives == null || negatives.Count == 0) return 0;
int inclusive = negatives[0];
int exclusive = 0;
for (int i = 1; i < negatives.Count; i++)
{
var min = Math.min(inclusive, exclusive);
inclusive  = exclusive + scalar × negatives[i];
exclusive = min;
}
return Math.min(inclusive, exclusive);

}

It may be interesting to note that scalar weight cannot be negative unless the count of included negatives is even.

Today we continue to review the book "From Smart to Wise" by Kaipa and Radjou. The authors say that "In our experience, wise leadership succeeds where smart leadership cannot." This book is about six capabilities which are essential for wise leadership and these are :
perpective, action orientation, role clarity, decision logic, fortitude and motivation. The leaders are classified as follows:
1) functional smart leaders and categorized as blue zone and
2) business smart leaders and categorized as red zone
The blue zone leaders are experts in their field. They execute effectively. They are risk-averse. They are detail oriented. They deliver exceptional results and they are efficient. Tim Cook is an example of this category
The red zone leaders are visionaries. They see the big picture. They are risk takers. They are very competitive. They are strategic entrepreneurs. They are highly motivated. Bill Gates is considered an example of this category.
Yesterday we read about what wise leaders do to apply the blue zone or the red zone technique as appropriate. Each of the capabilities was explained in this context and described. Today we read about how the blue zone and the red zone compare against each capability. The author states that the blue zone and red zone perspective is based on our knowledge and our experiences. With regard to finding the purpose, the blue zone focus on short term goals and execute it perfectly with like minded people's perspectives. They miss the subtle external changes and are not innovative outside their area of expertise.  The red zone perspective focus on long term goals, see the big picture,  are innovative and like blue zone also focus on like minded people's perspectives but they struggle to execute their grand vision. The authors quote Einstein as saying "one cannot solve a problem with the same mind-set that created it in the first place."
With regard to acting authentic and appropriate, the blue zone leaders focus on doing things the right way technically but not ethically. They follow a rule book or have a static style.  The red zone leaders are impulsive and follow their emotions. They need to feel successful and tend to believe that the ends justify the means.
With regard to role clarity, the blue zone leaders demonstrate leadership only in their domain of expertise and are willing to put emotions aside to fulfill their role. They get stuck in their role and can lose their identities. The Red zone leaders are very attached  to their role as a leader. They are emotional/passionate but they do not lose themselves within their role. To cultivate role clarity, each perspective could let go by cultivating a beginner's mind-set.
With regard to decision logic, blue zone leaders are cautious decision makers and better at short term decisions. They are open to feedback and tend to focus on validating comments. They rely on their instincts and take a long time to make decisions. The red zone leaders like high risk and thus high reward decisions. They make decisions quickly and are overconfident in their decision making capabilities. They don't pursue other viewpoints. The wise leaders operate in a grey zone. They exhibit "both clarity and pragmatism".
With regard to flexible fortitude, the functional smart leaders work very methodically, sometimes slowly and with limitations and boundaries. They are not very flexible and are stubborn but they end up completing high quality projects.  The smart zone leaders only care about projects  that lead to rewards and recognition. They can be moody but are not good at multitasking and tend to be resilient when faced with failures. Both type of smart leaders exhibit great fortitude but have their faults, only the wise show flexible fortitude.
#codingexercise
int GetMinSumNegatives(List<int>negatives)

{

if (negatives == null || negatives.Count == 0) return 0;
int inclusive = negatives[0];
int exclusive = 0;
for (int i = 1; i < negatives.Count; i++)
{
var min = Math.min(inclusive, exclusive);
inclusive  = exclusive + A[i];
exclusive = min;
}
return Math.min(inclusive, exclusive);

}