I would like to program a custom program or bootup procedure for my laptop that checks the computer's time, and either boots up as normal or displays a message if the current time is between X and Y, which either forces me to shut it down, or shuts down automatically.
Can this be done, and how do I do it?
Edit: My laptop is Windows.
Related
I am building a large project on a remote machine using Bazel. Clean build times are around 30 minutes. Incremental builds (changing code in 1-2 files) typically take around 10-20 seconds.
The problem I have is that when I log out of my machine and log back in again after 1-2 days the build command takes around 10 minutes even though I have not modified any source code.
If I call bazel shutdown and then call bazel build again the "no-build" op takes around 5-10 seconds (i.e. much better than the other "no-build" op).
If I log out and log back in again immediately I can see there is still a bazel process running in the background, which disappears when I call bazel shutdown. I am guessing that when I do not shut bazel down properly it gets killed in such a way that corrupts or deletes cached data. The long "no-build" op then spends a long time reconstructing data that was previously stored in the Bazel cache.
Is there a way to automatically shut down the bazel server when I am disconnected? Preferably this should work both when (i) I call exit from the command-line to log out, (ii) I get automatically disconnected through some kind of timeout or interruption in network connectivity.
Set up your development environment so that you sessions do not automatically exit / get killed, e.g., using a tool like screen or tmux. When you want to end a session call bazel shutdown prior to exit. Not completely automated but the point is that you should be in control of when your sessions end.
I'm using orchestrator to check if a collection of servers need to be rebooted. Here is my runbook:
The first activity will return multiple outputs with the ips of each server that I want to verify if they have a reboot pending. The next activity will invoke another runbook that only verifies if the server needs to be rebooted and that information will be added to a text file. The last activity will format some data.
(I need to check this information on two servers)
Right now the Get Hosts Name/IP runs once, the Reboot Pending activity runs twice (once for each server), and the last activity also runs twice.
I wanted to make the last activity only to run once, but I right now, no matter what I do it runs always twice.
I already tried to configure the Run Behavior Tab and Flattened the returned data. I did this in the Reboot Pending activity and the last activity. However, nothing seems to be working.
How can I make the last activity only run once after the activity before runs twice?
I used the Junction Activity and configured the Return data from
I have a standard situation, two distributed Erlang nodes, one master one standby.
When I stop the master the standby comes on - failover, when I start the master the standby stops - takeover. Everything works fine as long as heart is not turned on and there is no network split.
However, when I disconnect the master from the network after 60 seconds or so the standby gives me an error message ** removing (timedout) connection ** and starts up as if the master node stopped. This makes sense to me, it doesn't know if the master is alive or not, and epmd can't connect to the master node so it is removed from the nodes() list. Lets pretend for a moment that this is the desired outcome.
The problem is that, when the connection is restored, I have master and standby running at the same time and the standby is oblivious to the fact that the master is running. Pinging the standby during the masters init does not solve the issue. I checked nodes() on the standby after doing so, it sees the master node but still it continues to run.
My solution for now has been to create a process, that monitors all nodes that are above each node in hierarchy and if any of them are online, can be pinged, the process calls erlang:halt() to terminate the standby node. It works for simple situations, but maybe someone can tell me if there is a better way? I found a similar problem described on Elixir forum so it probably a known erlang problem without an easy solution. https://elixirforum.com/t/distributed-application-network-split/10007
If during a network split you don't want to have two nodes running in parallel I'm guessing an outside monitoring application needs to be used?
The second major issue is heart. If heart is turned on, as is, the failover never happens. If heart is running with a sleep before it calls start it stops the failover node when it calls the application start. So even when it can't start the master, do to it not having access to vital resources for example, it stops the failover node, and doesn't bring it back up after it fails to start the master. I don't know if heart is not supposed to be used with a distributed application or if there is an option to run some erlang code to check if the resources are available before attempting a start the node and before stopping the failover node?
The documentation on heart is not great. Very hard to find any examples of HEART_COMMAND. I found a way to set the HEART_COMMAND to a script from within my application, but there is a limit to how long the argument can be, and it's not as long as stated in the documentation from what I can tell. This for example sets a sleep timer for 60 seconds before calling application start again. It doesn't solve any issues, because in 60 seconds it stops the failover node and hangs if master node can't start.
heart:set_cmd("sleep 60; ./bin/myapp start")
The solution I've ended up with for now is letting heart of the main release start another release, a pre-loader, which does a preliminary check that all resources are available and if they are it starts the main release-application, and if they are not it continues checking forever. This way the main app is running on the failover node without interruption. So the main release has heart turned on, and the pre-loader does not. I ended up using a bash script file because I needed to do more work than I could fit in the heart:set_cmd/1, so I'm still calling heart:set_cmd(Dir ++ "/priv/myHeartScript.sh " ++ Arg1 ++ " " ++ Arg2), but don't get carried away with the Args as there is a limit on size! I also used Environment Variables which I set in vm.args using -env to pass data to the script, such as the pre-loader path/name. This allowed me to avoid having to edit the scrip too during deployment.
If anyone has a better solution PLEASE let me know.
UPDATE
The team at Erlang Solutions was kind enough to shed some light onto the subject. Basically, nobody they know uses the Erlangs built in distributed model. Everything revolves around the data, and as long as it is available on redundant databases you can spin up new applications anytime. They recommend using the cloud hosts that can spin up new servers when one goes down or use a redundant node design, so have 5 nodes up in parallel and if a few go down you can restart them manually or by other means.
As for me, I can say that getting heart to start a pre-loader release/app gets the job done but it gets complicated fast. To launch the app now requires provisioning several extra sys.config/vm.args/rebar.config files. I will be looking into their suggestions for the next iteration.
UPDATE
Moved away from using Erlang distributed model. Using RabbitMQ to send heartbeats to all nodes, including itself. If a node is receiving heartbeats from itself and no other node it's the master, if receiving more than one use any attribute like node name to chose the master. You don't have to use RabbitMQ, but you need to make sure all nodes can reach the same destination and consume from it.
Also, devOps oppose using heart. They prefer to use standard Linux tools to monitor application status and restart it after crash or a server reboot.
I have a Neo4J server running that periodically stalls out for 10s of seconds. The web frontend will say it's "disconnected" with the red warning bar at the top, and a normally instant REST query in my application will apparently hang, until the stall ends and then everything returns to normal. The web frontend becomes usable and my REST query completes fine.
Is there any way to debug what is happening during one of these stall periods? Can you get a list of currently running queries? Or a list of what hosts are connected to the server? Or any kind of indication of server load?
Most likely JVM garbage collection kicking in because you haven't allocated enough heap space.
There's a number of ways to debug this. You can for example enable GC logging (uncomment appropriate lines in neo4j-wrapper.conf), or use a profiler (e.g. YourKit) to see what's going on and why the pauses.
The last time I saw a data/partition node error it was because I launched the erlang shell which connected to the node on the same CPU via cookies etc. Immediately after startup the shell dumped the partition error on the screen. This is terribly bothersome....
how do I trap this exception?
how do I repair the exception programatically? (asked in another question)
how do I prevent this exception?
[update] I have two boxes that are running my Yaws application. The databases are replicated via Mnesia's extra_db_node feature. At some time after the servers are running I log into one of the boxes and launch 'erl' with a different sname and same cookie so that the 3 nodes can communicate. Shortly after the shell stabilizes and the shell prompt is displayed... a complex tuple is displayed on the screen indicating that there is a network partition error. This message appears to be a console dump rather than an exception that could be trapped by my yaws applications... but I want my yaws applications to detect the error and take corrective action.