How do photons travel at a speed that should be impossible to attain? If it requires infinite amount of energy to travel at the speed of light then how photon attains this speed? Its source is never infinitely sourced.
 A: According to special relativity
$$
\frac vc = \frac {pc}E = \frac {pc}{\sqrt{(mc^2)^2+(pc)^2}}
$$
For $m=0$ we have $pc=E$ and thus $v=c$, whereas for $m\not=0$ we have $pc<E$ and thus $v<c$.
A: Here is a good article on the mass of the photon, which answers your question.
http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html
The concept of relativistic mass is just a construct.  A particle only has one mass; its rest mass and it is constant.  It does not increase with particle velocity.  This article, The Concept of Mass, should help explain.  https://www.worldscientific.com/phy_etextbook/6833/6833_02.pdf
The Wikipedia article on "Mass in special relativity" is very good also.  
Here is a quote from an expert on the subject.

It is not good to introduce the concept of the mass $M = m\sqrt{1 - v^2/c^2}$ of a moving body
  for which no clear definition can be given. It is better to introduce
  no other mass concept than the ’rest mass’ m. Instead of introducing M
  it is better to mention the expression for the momentum and energy of
  a body in motion.

— Albert Einstein in letter to Lincoln Barnett, 19 June 1948
A: Massless particles don't need infinite energy to jump at $c$. Photons don't have rest mass as they don't interact with Higgs field.
What you have heard is applied only for mass. The whole thing works like this:
In relativistic physics, mass isn't constant. It is increased when its speed is increased. It is driven by this formula: $$m=\frac{M}{\sqrt{1-\left(\frac{v}{c}\right)^2}}$$ where, $m$ is relativistic mass, $M$ is rest mass, $v$ is speed.
So, at higher speed, we need higher energy to accelerate mass because it has been increased.
In case of massless particle, let's apply this formula:


*

*When $v$ is less than $c$: If you divide $0$ by a positive number, the result would be $0$. So, to accelerate $0$ relativistic mass particle, you wouldn't need energy. That's the reason why you can't find a massless particle at speed lesser than $c$.

*When $v$ is equal to $c$: Formula isn't valid because $0/0$ is not defined.
Note: While the answer is fine for general massless particle, it's not good for photons (ask relativistic physicists). Relativistic equations have $c$ due to the fact that it is a postulate of Einstein that photons already have this speed. So, it's not good for us to get to there in reverse.
So, answer for relativistic guys: Its framework for Relativistic Physics. We never needed to accelerate photons to $c$. It was already running at this speed.
A: 
If it requires infinite amount of energy to travel at the speed of
  light then how photon attains this speed

That's not quite right.  You're thinking of the energy required to accelerate a massive object to $c$ which is impossible thus the infinity.
However, there is no reference frame in which photons are at rest.  An object with speed $c$ in one frame has speed $c$ in all frames (thus the invariant speed).  
A: 
If it requires infinite amount of energy to travel at the speed of light then how photon attains this speed? Its source is never infinitely sourced.

Photons, like gluons, are massless particles. When we speak of 'massless', we mean the rest mass or invariant mass of an object. That is, this quantity is constant to all observers. Photons can travel in the speed of light c because of this property (being massless). If not, then it will require an infinite amount of energy to make a photon with mass travel at the speed of light.
