What exactly is 'proportionate'?

As you probably know from my Facebook and Twitter posts, I have recently downloaded the 'red alert' app, which sends a push notification every time a rocket is fired into Israel. About an hour ago, my phone couldn't keep up with the barrage of rockets that had been fired, with at least 80, reportedly, being fired into Israeli territory just today. Whilst Israelis run for cover, media outlets and Western politicians - as they did after the brutal murder of 3 Israeli teens last week - will call for Israel to act with restraint and no doubt accuse Israel of a disproportionate response. It is amazing how easy it is to clamber to the moral high ground when your starting place is a comfortable arm chair, sheltered (pun not intended) from the rocket fire that kills and injures Israelis. I ask two simple questions of everyone calling, perhaps with good intentions, on Israel to act with restraint:

1. What would you do? Just think about it for a minute.

2. What exactly is a proportionate response to indiscriminate rocket fire? Israel responds with targeted air strikes. Perhaps, simply returning rocket fire tit for tat would be proportionate?

I despair for the situation in the Middle East, truly I do. The cycle of violence looks like it is about to escalate, which will only lead to more needless Israeli and Palestinian deaths. (Initially that sentence read "deaths on both sides", but I decided to change it. This culture of "sides" and "us against them" is unhelpful.) What makes me irate, however, is people preaching at Israel, dictating what she should or should not do in response to attacks on her civilians, aimed at killing as many of them as possible.

I ask each and every one of you to download the app 'red alert'. Let your phone notifications reveal to you not only the joy of a new mention on twitter or a text from that person you're flirting with but also the horror and frequency of rocket fire into Israel. Perhaps you can change the sound to the actual alert sound thousands of Israelis will hear when you hear it, the only difference being they will run for cover and you will tell their government to act with restraint.

Update (8 July)

It has been pointed out to me that 'proportionately' does have a legal definition in international law. I must confess to not being aware of this, though initial research suggests that Israel is acting well within international law. What is important to make clear is that when I ask the question, I do so without reference to international law, knowing those who accuse Israel of disproportionate responses, make such accusations in the same way. When 'tweeter x' tells me Israel killed a Gazan woman and therefore did not act proportionately, s/he means that because Hamas are unsuccessful in their attempts to murder Israelis, Israel acts disproportionately when she responds and causes, regrettable, civilian casualties. S/he does not mean that Israel's act go against international law (though s/he may claim as much). Thus when I ask what would be a proportionate response, I do so (obviously) rhetorically but also in direct response to this individual. What exactly would be a proportionate response given Israel does act in accordance with international law? It is not enough for a response to be proportionate as far as international law is concerned for those who accuse Israel of disproportionate responses, so what exactly is proportionate?