How old is your Traeger? The hot rod (igniter) is considered to be a consumable/user replaceable part. However, it should last for a couple of years of service. You can get replacements at Ace Hardware, Home Depot and online.
What I have difficulty understanding, however, is why your fire went out after ignition. The way the controls are supposed to work is that when you press the ignite button, electricity will be sent to the hot rod to ignite the fire in the fire pot. However, once the fire is burning, the power to the hot rod is turned off and the heat from the fire in the burn pot continues the burn process until you shut the system down.
To troubleshoot the process, I suggest removing all the grates, drip tray, and flame shield from the unit. Clean out the burn pot, but do not reassemble the grill. First prime the auger. You should hear the auger turn and you should see/hear pellets drop into the burn pot for a couple of minutes. Then attempt to ignite the grill.. If all is well, the hot rod will turn red and the pellets in the burn pot will begin to smoulder. The fan will turn on and off intermittently to fan the smouldering embers into flame. Once the fire is burning brightly, the auger will start to feel pellets and the fan will blow to continue the fire. If things do not happen in this order, make notes of what you observe and contact Traeger Customer Service..
Also remember to check the connections for the auger motor, fan, and hot rod to the control panel to make sure nothing has loosened or become damaged.