Ejecting the parachute is usually done with a back powder charge. My people initially use "motor ejection" where as the motor is buring, it burns a delay grain (that provides tracking smoke also) and when it burns through, it contacts the ejection charge which pressurizes the body tube and push out the chute (one hopes).
Eventually, you want to use electronic ejection as the delay is sometimes hard to time exactly and you may have a chute come out too early or too late. And we typically like to add more complexities (electronics) to everything we do...
Anyway, this page isn't about the electronics, this is about what holds the black powder for the charge. I make up simple charge canisters out of 1/2" copper pipe. Then put an eye bolt throught them so that you can 'quick link' them near the altimeter. The red plug is called a "Caplug" and the 5/8" size fits perfectly. Of course in a rocket, you would have your igniter going into it as well. The picture worth a thousand words - these are some I just made up. They're soldered, but epoxy works as well to hold the cap on (and would be neater than my soldering job...). The duration of the black powder burn isn't long enough to burn the epoxy.
If the above isn't intuitively obvious - maybe this picture will help: