As of 2019/11, AWS charges $0.25 per million connection minutes. That sounds very innocent, but is it?
If your business grows and you have up to 1 million devices that needs to keep connected to an AWS Gateway, the cost, every month, just for the connection fee would be:
$0.25*1440*30*1M/1M = $10,800 per monthIn this case, a highly available cluster may be a lot more cost effective.
| Public Subnet | Private Subnet |
|---|---|
| Instances have public IP addresses | Instances do not have public IP address (selectable during instance creation) |
| Route table attached to the subnet has a default route | Route table attached to the subnet has no default route |
| Component | Default VPC | Nondefault VPC |
|---|---|---|
| Internet gateway | Yes | Yes, if you created the VPC using the first or second option in the VPC wizard. Otherwise, you must manually create and attach the internet gateway. |
| Route table with route to internet gateway for IPv4 traffic (0.0.0.0/0) | Yes | Yes, if you created the VPC using the first or second option in the VPC wizard. Otherwise, you must manually create the route table and add the route. |
| Route table with route to internet gateway for IPv6 traffic (::/0) | No | Yes, if you created the VPC using the first or second option in the VPC wizard, and if you specified the option to associate an IPv6 CIDR block with the VPC. Otherwise, you must manually create the route table and add the route. |
| Public IPv4 address automatically assigned to instance launched into subnet | Yes (default subnet) | No (nondefault subnet) |
| IPv6 address automatically assigned to instance launched into subnet | No (default subnet) | No (nondefault subnet) |
geom_bar first to plot a bar graph, and then use coord_polar to convert it to a pie chart. It works, but there is a catch:geom_bar sorts the fill value alphabetically and always put the lowest value one on the top of the bar graph. For example, “apple” would be on the top of “pear”. This becomes a problem if you intend to label the pie chart.dataframe in decreasing order by the fill variable. This way all calculations will be right.df=data.frame(val=c("z","b","c"),c2=c("b","d","f"),Freq=c(5,3,4))
df=df[order(df$val,decreasing=T),]
df$Label <- paste(df$val, paste(round((df$Freq/sum(df$Freq))*100,0),"%",sep=""), sep="-")
p <- ggplot(df,aes(x=1,y=Freq,fill=val))+geom_bar(stat="identity", color = "black")
p1 <- p + coord_polar(theta='y') + theme(axis.ticks=element_blank(),
axis.text.y=element_blank(),
axis.text.x=element_text(colour='black'),
axis.title=element_blank())
p2 <- p1 + scale_y_continuous(labels= df$Label,breaks=cumsum(df$Freq) - df$Freq/ 2)
p3 <- p2 + labs(title=title,fill=legend_title)+theme(plot.title = element_text(hjust = 0.5))
print(p3)
Update on 10/23/2019
This article explains the order issue very clearly:
https://sebastiansauer.github.io/ordering-bars/
In short, the rule for the sort order is:
- if factor, the order of factor levels is used
- if character, an alphabetical order is used
So one can change the factor order to change the plot order.
jq is a very useful tool to process JSON.
The idea of jq is centered on the idea of pipe and data stream.
Note below that a JSON entity is a self-contained and complete JSON object/array.
filter independently.-c (compact) flag to jq to print each stream as one line.. means the entire input data stream.[] moves into the JSON object/array one layer, and splits the data stream into multiple streams, one for each entry in the object or array. For example. {"a":1,"b":2} will broken into two data streams after passing this filter, becoming 1 and 2 respectively. Note that they are the values of the entires and are not valid JSON anymore, which is okay but needs to be noted. The same streaming-splitting will also happen for JSON arrays after passing this filter..["key"] generates one stream from the input stream. The shorthand is .key;, can be used to manually generate multiple streams.[ ] to generate an array, or use { } to generate an object. Note that to generate an object, one has to manually specify the keys, e.g.{"key1":.a, "key2":.b}, or use the shorthand {key1,key2} which is the same as {"key1":.key1,"key2":.key2};( ) can be used to instruct jq which part of the filter to be processed first, but it does not remove/combine/split the data streams.| has lower priority than ,. Therefore, 1,2,3|3 will produce three streams first 1,2,3, respectively, and then pass each stream to the second filter 3, with the end result of 3 streams of 3. If we use (), we can change that order. 1,2,(4|3) will process 4|3 first, generating 3, then processing 1,2,3, generating exact that as 3 streams of outoput. 1|4,2,3 will process 1 first, then passing to 4,2,3 three streams, causing the ending result to be 4,2,3 3 streams.length as $array_length | . to have jq remember a interim value and used in later stages of the filter..|.|.|.|. is the same as .map(x) takes an array as input, and outputs a new array, after running that filter for each element of the input array.select() function can be used to remove undesired streams. [1,2,3] | map(select(. >= 2)) will give you [2,3]if-then-else-end in the filter. Note that the else clause must be there. Sometimes the empty function can help.a//b The alternative operator can also be useful. It outputs a, if a is not false or null, otherwise it outputs b.input_filename can be used to find the input file name.numbers/objects/arrays/etc. to select results from multiple streamsTags: jq
~/.ssh/some_other_key.pub).scp some_other_key.pub intermediate:.ssh/
ssh-add -L | grep something_unique > ~/.ssh/some_other_key.pub
-i or IdentityFile.IdentitiesOnly yes (in .ssh/config or -o) to keep ssh from trying to offer any additional identities from your forwarded agent.%userprofile%\AppData\Local\Packages\Microsoft.Windows.ContentDeliveryManager_cw5n1h2txyewy\LocalState\Assets
https://www.howtogeek.com/247643/how-to-save-windows-10s-lock-screen-spotlight-images-to-your-hard-drive/
+----------------+
| |
| |
| FREE BUFFER |
| |
| |
+----------------+
| |
| UNSENT BYTES |
| |
+----------------+
| |
| UNACKED BYTES |
| |
+----------------+
Total send buffer size = unacked-bytes + unsent-bytes + free-buffer.
SO_SNDBUF socket option.
The buffer size could dynamically change its size as seen needed by the
OS. This works for both Linux and macOS. slen = sizeof(sndbufsiz);
err = getsockopt(sd, SOL_SOCKET, SO_SNDBUF, &sndbufsiz, &slen);
Total inflight bytes = unacked-bytes + unsent-bytes.
SO_NWRITE socket option on macOS, and SIOCOUTQ ioctl on Linux.int get_socket_used(int sd){
int err;
int used;
#ifdef __APPLE__
socklen_t slen = sizeof(used);
err = getsockopt(sd, SOL_SOCKET, SO_NWRITE, &used,&slen);
if(err < 0) {
perror("getsockopt 2");
exit(1);
}
#else
err = ioctl(sd, SIOCOUTQ, &used);
if(err < 0) {
perror("ioctl SIOCOUTQ");
exit(1);
}
#endif
return used;
}
TCP_INFO struct, but it is a private API.u_int32_t tcpi_snd_sbbytes; /* bytes in snd buffer including data inflight */
TCP_INFO structure, but the result is number of segments, or bytes. On macOS, TCP_INFO seems to contain this infomration (private API).int get_socket_unacked(int sd){
struct tcp_info tcp_info;
socklen_t tcp_info_length = sizeof(tcp_info);
if ( getsockopt(sd, IPPROTO_TCP, TCP_INFO, (void *)&tcp_info, &tcp_info_length ) == 0 ) {
return tcp_info.tcpi_unacked;
}
return 0;
}
//For macOS, use TCP_INFO
u_int64_t tcpi_txunacked __attribute__((aligned(8))); /* current number of bytes not acknowledged */
tcpi_notsent_bytes field of the TCP_INFO structure. NOTE that this requires kernel version to be 4.6 or newer. For Android that means Android 8 or newer. On Linux, it can also be obtained using SIOCOUTQNSD ioctl. It’s not clear how to do this on macOS.//defined in /usr/include/linux/sockios.h
int get_socket_unsent(int sd){
int err;
int unsent;
err = ioctl(sd, SIOCOUTQNSD, &unsent);
if(err < 0) {
perror("ioctl SIOCOUTQNSD");
exit(1);
}
return unsent;
}
//OR
int get_socket_unsent(int sd){
struct tcp_info tcp_info;
socklen_t tcp_info_length = sizeof(tcp_info);
if ( getsockopt(sd, IPPROTO_TCP, TCP_INFO, (void *)&tcp_info, &tcp_info_length ) == 0 ) {
return tcp_info.tcpi_notsent_bytes;
}
return 0;
}
unsent-bytes, when the TCP option TCP_NOTSENT_LOWAT is set. On macOS, kevent() doesn’t report socket as writable until the unsent TCP data drops below speciï¬ed threshold (typically 8 kilobytes). screen -S tunnel -d -m /path/to/tunnel.sh
That's all. This creates a background screen session, which runs the tunnel.sh script, which loops an ssh command to keep it up and running.