Once when I was living in my hometown, I found the IKEA bulb (5W827) in the table lamp heated very badly after half an hour of electricity, about 60 to 70 degrees Celsius. This type of bulb is made of plastic-coated aluminum shell. It seems that most plastic-coated aluminum shell LED are very hot, such as the opple 8W/860 LED bulb in my suspension lamp and the Philips 3.5W/865 LED bulb in my downlight.But spot lamps doesn't heat so seriously.

The heat rise upward, so when the LED lamp is at base-up, the LED heat is dissipates through the heatsink. At base-down, there is no dissipation of the heat of the LED, and it will fail shortly.
This is why I recommends to run CFLs with the base-down: The heat of the tube will rise upwards so the ballast won't be overheated. LED filament lamps are the same.

But my bulb base is mounted upwards.And most of my LED bulb heat seriously.

With this type the translucent dome temperature is completely irrelevant. What matters is the temperature of the (metal) "body" between the dome and socket. That section is the heatsink. And because it is thermally tied to the LEDs, as well as enclosing the ballast, the lamp position dheat oes not matter.
In fact with most LEDs the position does not matter either (as long as the cooling air can flow).
Unlike CFLs, where the part generating the heat (the tube) was something else than the thermally sensitive part (the ballast), with LEDs the heat generating and the most heat sensitive parts are the same thing, the LED chips alone, playing with the position won't help even when the LEDs would be thermally separated from the ballast.
So the only thing really helping is good airflow. So avoid light fixtures where the lamp is tight surrounded by an additional glas bowl or so. The best is really the free air (so e.g. with wall light where the bulb is covered by a sheet of glass just on the front and all the other sides are plain open,...)

But most of the fixtures have a seal glass shell.

Once when I was living in my hometown, I found the IKEA bulb (5W827) in the table lamp heated very badly after half an hour of electricity, about 60 to 70 degrees Celsius. This type of bulb is made of plastic-coated aluminum shell. It seems that most plastic-coated aluminum shell LED are very hot, such as the opple 8W/860 LED bulb in my suspension lamp and the Philips 3.5W/865 LED bulb in my downlight.But spot lamps doesn't heat so seriously.

There are leds designed to work at 85°C
https://datasheetspdf.com/pdf-file/1045679/CREE/CXA2011/1

87degC is pretty OK for LEDs, assume it is the really hottest spot temperature. The problem is, in many cheepeese designs their temperature tend to exceed even 150degC (I'm talking really about the hot spot on the LED die itself, not their substrate, chip carrier nor heatsink). Then mainly the bond wires (carrying the current to the die itself) tend to detach. Mainly the cathode one is most affected (the current direction plays a significant role here, it drags the metal ions along).

Not all fixtures are sealed, some (the better quality ones; speaking about really outdoor rated ones) have vents, just designed so when the water splash on it in any direction, it never goes any close to the electrical parts. But the truth is, with the molded plastic technology it is way cheaper to waterproof the fixture by designing it as "sealed" than making proper splash proof vents. So once the available plastic materials could handle the incandescent heat, many makers just went the cheaper way of "sealed" fixture designs.

But in real life these "sealed" fixtures are not as "sealed" as many would like to, the result is the water pooling inside and so keeping all the internals in a permanent high humidity, so corroding very fast. The vented fixture design may hot slightly wet when there is heavy rain combined with a crazy wind, but then it dries out very quickly, so at the end there is way less (or nearly no) corrosion damage even after decades of use.

I bought LED bulbs which have failed on me within a few months of use. I gather it's because the temps get to high at the base and fry the circuits/LED. 

The last one that fried on me was base up, exposed except for a plastic shell surrounding the top and it was in winter. Had enough so I ended up switching to a brand which boasts a 5 year warranty and I haven't had problems since. I don't know if the warranty means much or if they will refund if I use it, (I assume so because Australian refund laws are strong) but it does at least give me a little confidence they build their bulbs to last.